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AN  INTRODUCTION  TO  PHYSIOLOGY 


AN    INTRODUCTION 


TO 


PHYSIOLOGY 


BY 


WILLIAM   TOWNSi:ND   PORTER,  M.D. 

ASSOCIATE    PROFESSOR    OF    PHYSIOLOGY  IN    THE 
HAKVARO    MEDICAL   SCHOOL 


THE    UNIVERSITY    PRESS 

dambriligr,  ffflass. 
1901 


Copyright,  1900, 1901 
By  W.  T.  Porter 


PREFACE 

The  system  of  teaching  in  wliich  the  Introduc- 
tion to  Physiology  has  a  place  I  have  already 
described  in  the  Boston  Medical  and  Surgical 
Journal,  December  29,  1898,  and,  more  fully,  in 
the  Philadelphia  Medical  Journal,  September  1, 
1900.  Its  leading  principle  is  that  the  student 
shall  perform  for  himself  the  classical  experi- 
ments which  are  the  essence  of  the  science. 
Personal  observation  of  nature  is  the  dominant 
note.  It  is  the  function  of  the  instructor  to 
discuss  these  fundamental  observations  with  the 
student  and  to  add  such  related  facts  as  shall 
widen  the  student's  view. 

It  is  obvious  that  all  the  valuable  experi- 
ments in  physiology  cannot  be  performed  in  the 
time  that  is  ordinarily  given  to  this  subject.  A 
choice  must  be  made.  The  student  should  be 
trained  rather  than  informed.  The  trained 
observer  can  and  must  be  trusted  to  inform 
himself. 


VI  1'KKFACE 

Training  in  science  means  first  of  all  the 
mastery  of  one  field.  In  physiology  the  study 
of  nerve  ami  muscle  is  at  present  that  best 
adapted  t<>  form  the  mind  in  habits  of  exact 
observation  and  clear  reasoning.  Schooled  in 
this  important  part  of  physiology,  the  Btudent 
ran  pass  more  rapidly  and  with  greater  under- 
standing over  tli>'  remaining  parts.  Ii  is  with 
nerve  and  muscle,  therefore,  that  tin-  Introduc- 
tion to  Physiology  begins,  and  tip'  breatmenl  <>f 
this  Bubject  is  made  a-  thorough  as  is  practicable. 

There  are  in  ever]  chapter  in  physiology  im- 
portant experiments  which  for  various  reasons 
cannot  well  \»-  done  by  Btudents.  Thus  in 
1 '; i it  II.  "f  this  work,  treating  "f  the  circula- 
tion <»f  the  blood,  no  mention  is  made  "f  the 
if  Chauveau  and  Marey  upon  the  in- 
tracardiac   pressure.     It    i-    ex] ted   thai    the 

protocols  of  Buch  experiments  shall  be  provided 
;i-  uearly  as  possible  in  their  original  form 
Trained  by  his  own  observations,  the  Btudent 
will  then  find  profit  in  dealing  at  firs!  hand 
with  the  wort  <>f  < >t h-  r<. 

'I'll.-  apparatus  here  described  is  trustworthy 
:ind  relatively  inexpensive.  It  was  constructed 
under  my  direction  for  the  Btudents  who  per- 
form thi  riments  in   tie-  Harvard  M'dical 


PREFACE  Vll 

School.  Some  of  the  pieces,  for  example  the 
capillary  electrometer  and  the  artificial  scheme 
for  the  study  of  the  circulation,  are  wholly  of 
my  own  design.  Others  were  devised  with  the 
aid  of  past  and  present  instructors  and  mechan- 
ics in  the  Department  of  Physiology.  My  asso- 
ciates, also,  have  given  me  valuable  criticism, 
and  I  gratefully  acknowledge  their  many  kind- 
nesses. 

W.  T.  PORTER. 


CONTENTS 


i 

Page 

Introduction 3 

Preparation  of  gastrocnemius  muscle  —  Nerve-muscle  pre- 
paration. 

II 

Methods  of  Electrical  Stimulation 

Galvani's  Experiment 12 

The  Electrometer,  the  Rheocord,  and  the  Cell    .       14 
Surface  tension  —  Electrometer  —  Rheocord  —  Cell  —  Po- 
larization current  —  Dry  cell  —  Graduation  of  electrom- 
eter. 

Induction  Currents 30 

Magnetic  induction  —  Magnetic  field ;  lines  of  force  —  To 
produce  electric  induction,  lines  of  magnetic  force  must 
be  cut  by  circuit  —  Electromagnetic  induction  —  In- 
ductorium  —  Empirical  graduation  of  inductorium  — 
Make  and  break  induction  currents  as  stimuli  —  Extra 
currents  at  opening  and  closing  of  primary  current  — 
Tetanizing  currents  —  Induction  in  nerves  —  Exclusion 
of  make  or  break  current. 

Unipolar  Induction 44 

III 
The  Graphic  Method 51 


COX  TENTS 


IV 

The  Electrical  Stimulation  of   Muscle  and  Nerve 

Page 

The  Galvanic  Current 59 

Non-polarizable  electrodes  —  Opening  and  closing  contrac- 
tion—  Changes  in  intensity  of  stimulus. 

Polar  Stimulation  of  Muscle 65 

Ureter  —  Intestine  —  Tonic  contraction  —  Physiological 
anode  and  cathode  —  Polar  stimulation  in  heart. 

Polar  Stimulation  of  Nerve 75 

Law  of  contraction  —  Changes  in  irritability  —  Changes  in 
conductivity. 

Stimulation  of  Human  Nerves 89 

Stimulation  of  motor  points  —  Polar  stimulation  of  human 
nerves  —  Reaction  of  degeneration. 

Galvanotropism 98 

Paramecium. 

Influence  of  Duration  of  Stimulus 100 

Tonic  contraction  —  Rhythmic  contraction  —  Continuous 
galvanic  stimulation  of  nerve  may  cause  periodic  dis- 
charge of  nerve  impulses  —  Polarization  current  —  Polar 
fatigue  —  Opening  and  closing  tetanus  —Polar  excitation 
in  injured  muscle. 
Polar  Inhibition  by  the  Galvanic  Current  .     .     .     114 

Heart  —  Polar  inhibition  in  veratrinized  muscle. 
Stimulation  affected  by  the  Form  of  the  Muscle     117 
Effect  of  the  Angle  at  which  the  Current  Lines 

cut  the  Muscle  Fibres 118 

The  Induced  Current 119 

V 

Chemical  and  Mechanical  Stimulation 

Chemical  Stimulation 124 

Effect  of  distilled  water  —  Strong  saline  solutions  —  Dry- 
ing —  "  Normal  saline  "  —  Importance  of  calcium  — 
Constant  chemical  stimulation  may  cause  periodic 
contraction. 

Mechanical  Stimulation 127 

Idio-muscular  contraction. 


CONTENTS  BO 

VI 
Irritability  and  Conductivity 

Page 
Independent  irritability  of  mnscle  -Irritability  and  con- 
ductivity are  separate  properties  of  nerve  —  Minimal  and 
maxima]  stimuli;  threshold  value— Summation  of  in- 
adequate single  stimuli  —Relative  excitability  of  tlexor 
and  extensor  nerve  fibres;  Ritter-Rollett  phenomenon- 
Specific  irritability  of  nerve  greater  than  that  of  muscle  — 
Irritability  at  differenl  points  of  same  nerve  Excitation 
wave  remains  in  mnscle  or  nerve  fibre  in  wliich  it  starts 
—  Same  nerve  fibre  may  conduct  impulses  both  centrip- 
etally  and  centrifugally  —  Speed  of  nerve  impulse.  129 

VII 

The  Electromotive  Phenomena  of  Muscle  and 
Nerve 

The  Demarcation  Current  of  Muscle 150 

Demarcation  current  of  muscle  —  Stimulation  by  demarca- 
tion current  —  Interference  between  demarcation  cur- 
rent and  stimulating  current;  polar  refusal — Measure- 
ment of  electromotive  force  of  demarcation  current. 

Demarcation  Current  of  Nerve 159 

Nerve  may  be  stimulated  by  its  own  demarcation  current. 
Hypotheses  regarding   the  Causation  <>f  the  De- 
marcation Current 161 

Action  Current  of  Muscle 166 

Rheoscopic frog  — Action  current  in  tetanus;  stroboscopic 
method  —  Action  current  of  human  muscle  —  Action 
current  of  heart. 

Action  Current  of   Nerve 178 

Negative  variation  —  Positive  variation  —  Positive  after 
current  —  Contraction  secured  with  a  weaker  stimulus 
than  negative  variation  —  Current  of  action  in  optic 
nerve  —  Errors  from  unipolar  stimulation. 

Secretion  Current 183 

Secretion  current  from  mucous  membrane  —  Negative  vari- 
ation of  secretion  current. 


Xll  CONTENTS 

Page 
Electrotonic  Currents 186 

Negative  variation  of  electrotonic  currents  ;  positive  vari- 
ation  (polarization    increment)    of    polarizing   current. 
Electrotonic  current  as  stimulus. 
Electric  Fish 192 


VIII 

The  Change  in  Form 

Volume  of  Contracting  Muscle 194 

The  Single  Contraction  or  Twitch 195 

Muscle  curve  —  Duration  of  the  several  periods  —  Exci- 
tation wave  —  Contraction  wave  —  Relation  of  strength 
of  stimulus  to  fomi  of  contraction  wave  —  Influence  of 
load  on  height  of  contraction  —  Influence  of  temperature 
on  form  of  contraction  —  Influence  of  veratrine  on  form 
of  contraction. 

Tetanus 209 

Superposition  of  two  contractions  —  Superposition  in  teta- 
nus —  Muscle  sound  —  Relation  of  shortening  in  a  single 
contraction  to  shortening  in  tetanus. 

The  Isometric  Method 217 

Graduation  of  isometric  spring  —  Isometric  contraction. 

Contraction  of  Human  Muscle 220 

Simple  contraction  or  twitch  —  Isometric  contraction  — 
Artificial  tetanus  —  Natural  tetanus. 

Smooth  Muscle 221 

Spontaneous  contraction  —  Simple  contraction  —  Tetanus. 

The  Work  Done 223 

Influence  of  load  on  work  done  —  Absolute  force  of  mus- 
cle—  Total  work  done;  the  work  adder  —  Total  work 
done  estimated  by  muscle  curve  —  Time  relations  of 
developing  energy. 

Elasticity  and  Extensibility 229 

Elasticity  and  extensibility  of  a  metal  spring —  Of  a  rubber 
band  —  Of  skeletal  muscle  —  Extensibility  increased  in 
tetanus. 


244 


24S 
250 


CONTENTS  Xlll 

Page 

Fatigue °" 

Skeletal  muscle  of  frog  —  Hunan  skeletal  muscle. 

IX 
The  Mechanics  of  the  Circulation 

The  Artificial  Scheme 242 

The  Conversion  ok  the   Intermittent  into  a  Con- 
tinuous Flow 

Tiif.  Relation  between   Rate  of  Flow  and  Width 
of  Bi;i>       

The  Blood-Pressure 

Relation  of  peripheral  resistance  to  blood-pressure  — 
Curve  of  arterial  pressure  in  the  frog  —  Effect  ou  blood- 
pressure  of  increasing  the  peripheral  resistance  in  the 
f10g  —  Changes  in  the  stroke  of  the  pump ;  iuhibition 
of  the  ventricle  —  Effect  of  inhibition  of  the  heart  on 
the  blood-pressure  in  the  frog. 

The  Heart  as  a  Pump 255 

Opening  and  closing  of  the-  valves  —  Period  of  outflow 
from  the  ventricle  —  Visible  change  in  form  — Graphic 
record  of  ventricular  contraction. 

The  Heart  Muscle       258 

All  contractions  maximal  —  Staircase  contractions  —  Iso- 
lated apex  ;  Bernstein's  experiment  —  Rhythmic  con- 
tractility of  heart  muscle  — Constant  stimulus  may  cause 
periodic  contraction  —  Inactive  heart  muscle  still  irri- 
table—  Refractory  period ;  extra  contraction;  compen- 
satory pause—  Transmission  of  the  contraction  wave 
in  the  ventricle  ;  Engelmann  s  incisions  — Transmission 
%  of  the  cardiac  excitation  from  auricle  to  ventricle; 
Gaskell's  block  — Tonus  —  Influence  of  load  on  ventri- 
cular contraction  —  Influence  of  temperature  on  frequency 
of  contraction  —  Action  of  inorganic  salts  (sodium,  cal- 
cium, potassium)  on  heart  muscle. 

1  The  Heart  Sounds 269 

The  Pressure-Pulse 271 

Frequency  —  Hardness  —  Form  —  Volume  —  Pressure- 
pulse  curve  in  the  artificial  scheme  —  Human  pressure- 
pulse  curve  —  Low  tension  pressure-pulse  —  Pressure- 


XIV  CONTENTS 

Page 
pulse   in    aortic  regurgitation  —  Stenosis  of  the  aortic 
valve  —  Incompetence  of  the  mitral  valve. 
The  Volume  Pulse 280 

X 

The  Innervation  of  the  Heart  and  Blood  Vessels 

The  Augmentor  Nerves  of  the  Heart 283 

Preparation  of  the  sympathetic  —  Action  of  sympathetic 
on  heart. 

The  Inhibitory  Nerves  of  the  Heart 286 

Intracardiac  inhibitory  mechanism  ■ —  Preparation  of  the 
vagus  nerve  —  Stimulation  of  cardiac  inhibitory  fibres 
in  vagus  trunk  —  Effect  of  vagus  stimulation  on  the 
auriculo-veutricular  contraction  interval  —  Irritability 
of  the  inhibited  heart  —  Intracardiac  inhibitory  mech- 
anism —  Inhibition  by  Stannius  ligature  —  Action  of 
nicotine  —  Atropine  —  Muscarine  —  Antagonistic  action 
of  muscarine  and  atropine. 

The  Centres  of  the  Heart  Nerves 292 

Inhibitory  centre  —  Augmentor  centre  —  Reflex  inhibition 
of  the  heart ;  Goltz's  experiment  —Reflex  augmentation. 

The  Innervation  of  the  Blood  Vessels  ....  296 
Bulbar  centre —  Vasomotor  functions  of  the  spinal  cord  — 
Effect  of  destruction  of  the  spinal  cord  on  the  distri- 
bution of  the  blood  —  Vasomotor  fibres  leave  the  cord 
in  the  anterior  roots  of  spinal  nerves  —  Vasoconstrictor 
fibres  in  the  sciatic  nerve  —  Vasodilator  nerves  —  Reflex 
vasomotor  actions. 


ILLUSTRATIONS 

Diagrams  which  merely  illustrate  the  grouping  of  apparatus  for  a  par- 
ticular experiment  are  omitted  from  this  list. 

Fig.  Page 

1.  Muscles  of  left  hind  limb  of  frog,  dorsal  view       .     .  7 

2.  Nerve-muscle  preparation 8 

3.  Muscle  clamp,  stand,  and  nerve-holder       ....  9 

4.  Capillary  electrometer 18 

5.  Rbeocord 20 

7.      Pole-changer 25 

9.     Inductorium,  simple  key,  and  platinum  electrodes    .  31 

11.  Kymograph 51 

12.  Tuning-fork 55 

13.  Moist  chamber,  with  non-polarizable  electrodes,  and 

muscle  lever 60 

14.  Hind  limb  of  frog,  anterior  view 62 

17.  Cork  clamp 65 

18.  Electromagnetic  signal 68 

25.  Motor  points  on  the  anterior  surface  of  the  forearm 

and  hand 90 

26.  Motor  points  on  the  posterior  surface  of  the  forearm 

and  hand 91 

31.  Frog-board        115 

32.  Gas  chamber,    with   bottle   for  generating    carbon 

dioxide 135 


XVI  ILLUSTRATIONS 

Fig.  Page 

33.  Sartorius 144 

34.  Gracilis 145 

38.  Scheme  of  myomeres  in  a  parallel-fibred  muscle  .     .  162 

39.  Scheme  of  myomeres  in  an  oblique  section       .     .     .  163 

40.  Wheel  interrupter      .     . 167 

42.  Heart-holder 174 

43.  Scheme  of  differential  rheotome 176 

47.  Volume  tube 195 

48.  Rigid  muscle  lever     . 205 

49.  "  Muscle  warmer " 206 

50.  Ergograph 220 

51.  Work  adder 225 

52.  Artificial  scheme  of  circulation 243 

53.  Mercury  manometer 252 

54.  Sphygmograph 256 

55.  Scheme  of  sympathetic  nerve  in  frog 284 

56.  Scheme  of  cervical  nerves  in  frog 286 

57.  View  of  brain  of  frog  from  above 293 


PART   I 

THE  PHYSIOLOGY  OF  MUSCLE  AND 
NERVE 


PART  I 

THE   PHYSIOLOGY   OF   MUSCLE   AND 
NERVE 


INTRODUCTION 

Until  recent  times  it  was  believed  that  many  of 
the  compounds  found  in  the  tissues  of  animals 
and  plants  could  be  made  only  by  the  action  of 
organized,  i.  e.  living  matter.  Such  compounds 
were  called  organic  to  distinguish  them  from 
those  found  in  inorganic  or  inanimate  nature. 
The  forces  producing  organic  compounds  were 
thought  to  be  partly  the  ordinary  chemical 
and  physical  processes  known  to  science,  and 
partly  certain  mystical  agencies  termed  vital 
forces.  The  great  discovery  of  "YVohler  in 
1828  that  urea  (C02NH2),  a  typical  organic 
compound,  could  be  made  synthetically  in  the 
laboratory,  overthrew  this  conception  and  was 
the  beginning  of  a  long  and  fruitful  struggle  to 


4       THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

bring  the  phenomena  of  living  matter  within 
the  operation  of  chemical  and  physical  laws 
without  recourse  to  the  supernatural  and  occult. 
According  to  this  new,  unified  view  of  nature, 
which  is  the  foundation  of  modern  physiology, 
all  phenomena,  whether  animate  or  inanimate, 
are  alike  the  expression  of  chemical  and  physi- 
cal processes,  some  known,  some  unknown,  none 
of  which  is  fundamentally  different  from  the 
rest. 

The  physiologist,  therefore,  now  looks  upon 
the  reactions  of  living  matter  with  the  eye 
of  the  physicist,  and  it  is  of  the  first  impor- 
tance to  beginners  in  physiology  to  acquire  this 
point  of  view.  To  get  the  physical  point  of 
view  it  is  necessary  to  master,  as  thoroughly  as 
may  be,  some  part  of  physiology,  the  physics  and 
chemistry  of  which  are  well  advanced.  It  m 
necessary,  too,  that  the  field  selected  for  investi- 
gation should  be  one  in  which  material  is  both 
abundant  and  easy  of  access.  No  part  of  physio- 
logical science  fulfils  these  conditions  so  well 
as  that  which  deals  with  the  phenomena  of 
muscle  and  nerve. 

Let  us  begin  by  examining  one  of  the  skeletal 
muscles  of  the  frog. 

The  Preparation  of  the  Gastrocnemius  Muscle. 
—  Wrap  the  frog   in   the  cloth,  the   head  out. 


INTRODUCTION  5 

Pass  one  blade  of  the  stout  scissors  between  the 
jaws,  Bring  this  blade  to  the  angle  of  the  jaw, 
the  other  blade  over  the  junction  of  the  head 
and  trunk.  Cu^  off  the  skull  with  a  single 
closure  of  the  scissors.  Thrust  the  pithing 
wire  into  the  cranial  cavity  and  then  into  the 
vertebral  canal,  destroying  the  brain  and  spinal 
cord.  The  frog  ceases  to  move  ;  the  muscles  are 
relaxed.  Sever  the  skin  of  the  foot  by  a  circular 
incision  at  the  distal  end  of  the  tendo  Achillis. 
Reflect  the  skin  upon  itself  until  the  whole  of 
the  gastrocnemius  muscle  is  exposed.  Do  not 
lay  the  bared  leg  on  the  table  or  permit  it  to 
touch  the  skin  of  the  other  leg.  The  skin  of  the 
frog,  like  that  of  the  salamander  and  some  other 
batrachians,  is  provided  with  a  protective  secre- 
tion injurious  to  sensitive  tissues.  Place  the 
frog  on  the  table,  back  uppermost,  with  the  bared 
leg  resting  across  the  corner  of  a  glass  plate  at 
the  edge  of  the  table  in  such  a  way  that  the 
foot  is  flexed,  i.  e.  hangs  down  over  the  edge  of 
the  table.  Pinch  the  muscle  sharply  with  the 
forceps. 

The  muscle  passes  into  the  active  state;  it 
shortens  and  thickens.  The  foot,  which  is  rela- 
tively less  fixed  than  the  leg,  is  extended.  The 
contraction  is  followed  by  a  slower  relaxation  or 
return  to  the  original  form. 


6   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEKVE 

Observe  that  the  mechanical  act  of  pinching 
caused  the  resting  muscle  to  become  active. 
Its  stored  energy  was  transformed  into  external, 
mechanical  work,  i.  e.  the  moving  of  the  foot. 
Not  all  of  the  energy  set  free  takes  this  easily 
visible  form.  It  will  be  shown  later  that  much 
of  it  is  made  active  as  molecular  motion,  in  the 
form  of  heat,  chemical  action,  and  electricity. 
Agents  which  occasion  a  transformation  of 
energy  within  the  living  body  are  termed  stim- 
uli, and  tissues  which  convert  energy  of  one 
form  into  energy  of  another  in  consequence  of 
stimulation  are  said  to  be  irritable.  All  living 
tissues  are  alike  irritable,  but  the  form  in  which 
their  kinetic  or  active  energy  appears  differs 
with  the  nature  of  the  tissue.  The  contrast 
between  muscle  and  nerve  in  this  respect  is 
very  instructive. 

The  Nerve-Muscle  Preparation.  —  Divide  the 
body  transversely  behind  the  fore  limbs.  Re- 
move the  viscera.  Seize  the  spinal  column  with 
the  finger  and  thumb  of  one  hand,  and  the 
skin  of  the  back  with  the  other  hand,  covered 
with  a  cloth  to  prevent  slipping.  Draw  the  hind 
limbs  out  of  the  skin.  Lay  the  frog  down,  back 
uppermost.  Note  on  the  outside  of  the  thigh 
the  triceps  femoris  muscle  ;  on  the  median  side, 
the  semi-membranosus ;  between  these,  the  nar- 


INTRODUCTION 


bi 


row  biceps  femoris.    (Fig.  1.)    Cautiously  divide 
the    connective  tissue    between    the    senii-niem- 
branosus    and  the  biceps  femoris.     On  drawing 
these    muscles    apart, 
the  sciatic  nerve  and 
the     femoral    vessels 
will  be   seen.      Clear 
the  nerve    with    scis- 
sors and  forceps  from    "" 
the  knee  to  the  ver-    tr. 
tebral    column.      The 
nerve     itself     should 
not  be   touched   with 
the  instruments.  Near 
the   pelvis  it  will  be 
necessary  to  divide  the 
pyriform  and  the  ilio- 
coccygeal   muscles: 
carefully     avoid     the     „         „     ,      ,,„,.,,.,., 

J  Fig.  1.    Muscles  of  left  hmd  limb  of 

nerve      While       doilllT  fl'°£.  dorsal  view  (Ecker  and  Wieders- 

lieiiu). 

this. 

Lift  the  tip  of  the  urostyle  (the  tenth  verte- 
bra, a  long,  slender  bone  which  forms  the  caudal 
end  of  the  vertebral  column)  with  the  forceps, 
and  remove  the  bone  as  far  as  the  last  lumbar 
vertebra.  Divide  the  spinal  column  transversely 
between  the  6th  and  7th  lumbar  vertebra?.  Turn 
the    frog  back  down.     "With  the  stout   scissors 


8       THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 


bisect  lengthwise  the  7th,  8th,  and  9th  vertebrae. 
Grasp  the  half  from  which  the  prepared  nerve 
springs  and  lift  it  gently,  freeing  the  nerve  with 
the  scissors  down  to  the  knee. 

Pass  now  to  the  leg.  Cut  through  the  Achil- 
les tendon  of  the  gastrocnemius 
muscle  below  the  thickening  at 
the  heel.  Free  the  muscle  up 
to  its  origin  from  the  femur,  tak- 
ing care  not  to  harm  the  branch 
of  the  nerve  which  enters  the 
muscle  on  its  posterior  surface 
near  the  knee.  Cut  through  the 
tibia  about  one  centimetre  from 
the  knee-joint.  Clear  away  the 
muscles  of  the  thigh  from  the 
lower  end  of  the  femur,  avoiding 
the  sciatic  nerve.  Cut  through 
the  femur  about  its  middle.  (Fig. 
2.)  Lay  the  sciatic  nerve  for 
safety  along  the  gastrocnemius 
muscle.  Fasten  the  lower  frag- 
ment of  the  femur  in  the  jaws  of  the  muscle 
clamp.  Let  the  whole  nerve  rest  without 
stretching  on  the  nerve-holder,  the  filter  paper 
covering  which  should  be  moistened  with  normal 
saline  solution  (0.6  per  cent  NaCl).  Take  care 
that  the  nerve  does  not  dry  between  the  nerve- 


Fig.  2.  Nerve-mus- 
cle preparation;  gas- 
trocnemius muscle 
and  sciatic  nerve.  F, 
end  of  femur ;  N,  sci- 
atic nerve  ;  I,  tendo 
Achillis  ;  t1,  attach- 
ment of  smaller  ten- 
don of  gastrocnemius 
to  femur  (Handbook 
for  the  Physiological 
Laboratory). 


IXTRODUt.TI'  IN 


g 


holder  and  the  muscle.    (Fig.  3.)    Pinch  the  end 
of  the  nerve. 


Fig.  3.  The  muscle  clamp,  stand,  and  nerve-holder.  The  nerve-hoMer 
supports  the  sciatic  nerve,  together  with  the  portion  <>f  the  spinal  column 
from  which  it  springs.  The  handle  of  the  nerve-holder  is  of  thick  lead 
win-  which  may  be  bent  as  desired.  The  binding  post  on  the  muscle  clamp 
provides  electrical  connection  with  the  upper  end  vt  the  m 

No  change  will  be  seen  in  the  nerve,  hut  the 
muscle  will  contract. 

Thus,  while  the  most  conspicuous  form  which 


10      THE    PHYSIOLOGY   OF   MUSCLE   AND    NEKVE 

the  energy  of  muscle  takes,  when  set  free,  is 
mechanical,  the  active  nerve  does  not  alter  its 
form,  but  spends  its  energy  in  a  molecular  change, 
the  nerve  impulse,  which  passes  from  point  to 
point  along  the  nerve  to  the  muscle,  or  gland,  or 
other  structure  connected  functionally  to  the 
nerve.  The  effect  produced  by  the  nerve  impulse 
depends  on  the  nature  of  the  tissue  in  which  the 
nerve  ends  ;  for  example,  the  energy  set  free  in 
secreting  glands  is  especially  chemical ;  that  set 
free  in  the  electrical  organ  of  Torpedo  is  espe- 
cially electrical.  In  considering  these  illustra- 
tions of  the  ways  in  which  the  energy  of  living 
tissue  may  be  set  free,  however,  two  facts  should 
always  be  kept  in  mind;  first,  that  by  far  the 
greater  part  of  the  stored  energy  of  the  body  is 
set  free  as  heat ;  and  secondly,  that  while  the 
several  tissues  are  characterized  by  the  especial 
prominence  of  some  one  form  of  energy,  as  con- 
tractility in  the  case  of  muscle,  and  the  pro- 
duction and  conveyance  of  a  nerve  impulse  in 
the  case  of  nerve,  yet  the  transformation  of 
energy  in  each  tissue  is  a  complex  process,  many 
steps  of  which,  for  example,  heat  and  chemical 
action,  are  common  to  all  living  substance. 

We  have  made,  then,  the  fundamental  obser- 
vation that  an  adequate  stimulus  will  occasion 
in    muscle  a  conversion    of    latent  energy  into 


INTRODUCTION  11 

mechanical  change  in  form,  and  in  the  nerve  a 
molecular  change  that  passes  along  the  nerve  as 
a  nerve  impulse.  We  must  now  examine  sys- 
tematically the  usual  methods  of  exciting  the 
transformation  of  energy  and  inquire  concerning 
their  effect  on  muscle  and  nerve. 

Apparatus 

Normal  saline.  Bowl.  Cloth.  Pithing  wire.  Scissors. 
Forceps.  Pipette.  Glass  plate.  Cement.  Foil.  Nerve 
holder  (filter  paper).     Muscle  clamp.     Stand.     Frog. 


12   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 


II 

METHODS  OF  ELECTRICAL  STIMULATION 

The  stimulus  most  usually  employed  in  the 
laboratory  is  electricity,  because  electricity  will 
stimulate  when  used  in  quantities  which  do  not 
destroy  the  tissues,  as  do  many  mechanical,  chem- 
ical, and  thermal  stimuli,  and  because  the  inten- 
sity and  duration  of  the  electrical  stimulus  can 
be  graduated  with  accuracy.  It  will  be  neces- 
sary, therefore,  to  study  with  especial  care  the 
methods  of  electrical  stimulation. 

Galvani's  Experiment 

Eest  a  copper  wire  on  the  gastrocnemius 
muscle  and  a  zinc  wire  on  the  sciatic  nerve  of 
a  nerve-muscle  preparation.  Bring  the  other 
ends  of  the  wires  into  contact. 

The  muscle  will  twitch. 

Galvani  supposed  that  the  muscle  itself  pro- 
duces the  electricity  that  stimulates  it  in  this 
experiment.     Volta  pointed  out  that  when  two 


METHODS   OF   ELECTRICAL   STIMULATION         13 

dissimilar  metals  are  brought  into  contact, 
one  becomes  positively,  and  the  other  i 
lively  electrified.  The  chief  source  of  electrical 
energy  in  this  experiment,  however,  is  derived 
not  from  the  contact  of  two  dissimilar  metals 
with  each  other,  but  from  their  contact  with 
a  decomposable  liquid,  namely,  the  saline  solu- 
tion which  forms  the  principal  part  of  animal 
tissue.  Such  saline  solutions  are  now  supposed 
by  physical  chemists  to  contain  dissociated  atoms 
(or  groups  of  atoms)  called  ions  each  of  which 
carries  a  strong  charge  of  electricity.  When  the 
metals  in  contact  with  the  liquid  are  joined, 
the  ions  begin  to  move  through  the  liquid. 
Those  wandering  fiom  the  point  at  which 
the  electrical  energy  is  greatest  ( termed  the 
point   of   highest  potential,1   or  anode)  towards 

1  The  difference  of  potential  may  be  compared  to  the  differ- 
ence of  water  level  between  a  reservoir  and  its  distribnting 
pipes.  It  produces  an  electromotive  force,  comparable  to  the 
force  which  moves  the  water  from  the  higher  to  the  lower  level. 
The  unit  of  electrical  pressure  is  the  volt.  The  flow  through 
an  hydraulic  system  is  measured  by  the  quantity  of  water  pass- 
ing any  point  in  a  given  time  ;  similarly  the  quantity  of  elec- 
tricity is  the  amount  that  flows  through  a  cross- section  of  the 
conductor  in  a  given  time.  The  unit  of  quantity  is  the  ampere. 
Electricity  parsing  through  a  conductor  meets  with  a  resistance 
which  becomes  greater  as  the  cross-section  of  the  conductor 
diminishes,  just  as  water  can  be  forced  more  easily  through 
wide  chaunels  than  through  narrow  ones.     The  unit  of  electri- 


14      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

the  point  of  lowest  potential,  or  cathode,  are 
termed  "  cations  "  {Kara,  down) ;  and  those  mov- 
ing from  the  lowest  to  the  highest  potential  are 
termed  "  anions  "  (avd,  up).  Examples  of  anions 
are  C1-,  Br,  I-  OH-,  N02-,  NOs-,  C103-,  S04-",  etc. ; 
of  cations :  most  of  the  metals,  H+,  NH4+,  etc. 
Chemically  equivalent  ions  carry  equal  quantities 
of  positive  or  negative  electricity.  The  more 
swiftly  the  ions  move,  the  greater  will  be  the 
quantity  of  electricity  which  they  will  transport 
in  a  unit  of  time. 


The  Electrometer,  the  Eheocord,  and 
the  Cell 

In  order  to  study  differences  in  electrical 
potential,  a  galvanometer  or  some  other  elec- 
trometer is  necessary.     In  the  galvanometer,  the 

cal  resistance  is  the  ohm.     The  precise  definition  of  these  units 
is  as  follows  :  — 

A  volt  is  the  electromotive  force  that,  steadily  applied  to  a 
conductor  whose  resistance  is  one  international  ohm,  will  pro- 
duce a  current  of  one  international  ampere.  The  practical 
ampere  is  the  unvarying  current,  which,  when  passed  through 
a  solution  of  nitrate  of  silver  in  water,  deposits  silver  on  the 
cathode,  or  negative  pole,  at  the  rate  of  0.001118  gram  per 
second.  The  ohm  is  the  resistance  offered  to  an  unvarying 
electrical  current  by  a  column  of  mercury  at  the  temperature 
of  melting  ice,  14.4521  grams  in  mass,  of  a  constant  cross-sec- 
tional area,  and  of  the  length  of  106.3  centimetres. 


METHODS   OF   ELECTRICAL   STIMULATION         15 

points  of  different  potential  are  connected  by  a 
coil  of  wire  near  which  is  suspended  a  magnet. 
When  the  circuit  is  completed,  the  electrical 
energy  acts  on  the  suspended  magnet  by  induc- 
tion, and  deflects  it  to  an  extent  proportionate 
to  the  difference  of  potential.  In  the  capillary 
electrometer,  which  is  the  electrometer  preferred 
here,  a  capillary  tube  filled  with  mercury  and 
sulphuric  acid  dips  in  a  wider  tube  which  con- 
tains sulphuric  acid.  The  points  the  potential 
of  which  is  to  be  measured  are  connected  with 
the  mercury  and  the  acid  respectively.  When 
the  connection  is  made,  the  tension  of  the  surface 
of  mercury  in  contact  with  the  acid  changes, 
causing  the  mercury  to  move  in  the  capillary. 
The  change  in  surface  tension  is  proportional  to 
the  difference  in  potential.  The  action  of  the 
instrument  will  be  more  clear  from  the  follow- 
ing experiments. 

Surface  Tension.  —  In  a  small  porcelain  evap- 
orating dish  place  a  globule  of  mercury  about 
one  inch  in  diameter. 

The  cohesion  of  the  mercury  is  stronger  than 
the  attraction  between  the  mercury  and  porcelain, 
—  the  mercury  does  not  "wet"  the  porcelain. 
The  free  surface  of  the  mercury  is  curved  and 
not  plane,  as  it  would  be  were  the  molecules 
acted  upon  by  the  force  of  gravity  alone.     Obvi- 


16   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEEVE 

ously  the  spreading  of  the  mercury  is  resisted 
by  some  force  that  strives  to  make  the  drop 
spherical,  i.  e.  to  make  the  surface  as  small  as 
possible. 

This  force  is  called  the  surface  tension.  It  is 
the  attraction  which  the  molecules  beneath  the 
surface  exert  on  the  side  of  the  surface  layer 
next  them.  The  form  of  the  drop  is  the  result 
of  the  equilibrium  between  these  opposing  forces 
(Thomas  Young,  1804). 

Surface  tension  altered  by  electrical  energy.  — 
Cover  the  mercury  one  centimetre  deep  with  5 
per  cent  sulphuric  acid.  Note  carefully  the 
degree  of  convexity.  Add  a  trace  of  potassium 
chromate.     The  drop  will  flatten  slightly. 

When  a  metal  is  placed  in  an  electrolyte,  a 
difference  of  potential  is  created  at  the  surfaces 
in  contact.  If  the  metal  is  positive  compared 
with  the  electrolyte,  an  immeasurably  thin  layer 
of  positively  electrified  molecules  may  be  said  to 
coat  its  surface,  and  in  the  electrolyte  a  parallel 
layer  of  negatively  electrified  molecules  will 
collect.  On  every  side  of  the  parallel  layer 
electricity  of  the  same  sign  will  be  repelled.  In 
the  case  of  a  liquid  metal,  for  example  mercury, 
the  form  of  the  surface  will  be  altered,  for  the 
repulsion  of  like  electricities  will  tend  to  stretch 
the  surface  layer,  and  will  thus  oppose  the  sur- 


METHODS   OF   ELECTRICAL   STIMULATION        17 

face  tension.  The  new  form  which  the  surface 
will  take  is  the  equilibrium  between  the  electri- 
cal energy  and  the  surface  tension  (Helmholtz). 
If  this  equilibrium  is  changed  by  the  introduction 
of  new  electrical  energy,  the  curvature  of  the 
surface  will  change  (Henry). 

Fasten  an  iron  wire  in  the  muscle  clamp  and 
clamp  the  latter  to  the  stand.  Bring  the  wire 
over  the  mercury  and  lower  the  muscle  clamp 
until  the  wire  just  touches  the  edge  of  the 
mercury.     Fix  the  clamp  in  this  position. 

The  instant  the  two  metals  touch  (iron  and 
mercury  in  chromic  acid  solution)  the  mercury 
will  become  positive  towards  the  iron.  The 
existing  difference  of  potential  will  be  altered. 
The  surface  tension  will  thereby  be  increased 
and  the  globule  will  become  more  convex. 
This  movement  withdraws  the  margin  of  the 
globule  from  the  iron  and  the  globule  flattens 
again,  which  brings  it  again  into  contact  with 
the  iron.  This  play  is  repeated  until  the  chromic 
acid  is  all  reduced  to  chromic  sulphate. 

The  Electrometer.  —  The  electrometer  consists 
of  a  vertical  tube  drawn  out  at  the  lower  end 
into  a  fine  capillary  and  filled  with  mercury. 
(Fig.  4.)  The  upper  end  of  the  tube  is  joined 
to  a  rubber  bulb,  by  the  compression  of  which 
pressure  can  be  made  on  the  mercury  column ; 
2 


18      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

a  side  branch  leads  to  a  mercury  manometer 
which  records  the  amount  of  this  pressure. 
The  end  of  the  capillary  dips  in  a  reservoir  con- 


rig.  4.   The  capillary  electrometer. 


taining  20  per  cent  sulphuric  acid.  A  little 
mercury  is  placed  in  the  reservoir.  Platinum 
wires  lead  from  this  mercury   and  that  in  the 


METHODS    OF   ELECTRICAL    STIMULATION         19 

capillary  to  convenient  binding  posts.  When 
mercury  is  placed  in  the  vertical  tube  it  enters 
the  capillary  until  the  weight  of  the  column  of 
mercury  is  balanced  by  the  surface  tension, 
which  is  inversely  proportional  to  the  diameter 
of  the  tube.  If  the  capillary  is  now  dipped  in 
the  reservoir  containing  the  sulphuric  acid  and 
the  rubber  bulb  compressed,  mercury  will  be 
forced  out  of  the  capillary  into  the  acid,  and  on 
lowering  the  pressure  the  mercury  will  retreat 
within  the  capillary,  drawing  the  acid  after  it. 
As  the  mercury  in  the  capillary  is  kept  from 
falling  by  the  surface  tension,  it  is  obvious  that 
whatever  increases  or  diminishes  the  surface 
tension  will  raise  or  lower  in  corresponding 
measure  the  mercury  in  the  capillary.  The 
alteration  in  surface  tension  is  accompanied  by 
the  movement  of  ions  between  the  meniscus 
and  the  remaining  electrode  of  the  electrometer 
(the  mercury  in  the  acid  reservoir).  In  practice 
it  is  found  that  this  movement  can  be  neither 
very  rapid  nor  long  continued,  without  injuring 
the  sensitiveness  of  the  instrument.  The  po- 
tential difference  from  even  a  single  element 
(Daniell  or  dry  cell)  is  far  too  large  to  be  used 
safely.  It  is  advisable  to  employ  a  potential 
divider,  or  rheocord,  which  shall  permit  only  a 
fraction  of  the  original  potential  (not  more  than 
0.1  volt)  to  reach  the  electrometer. 


20      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

The  Rheocord.  —  If  two  poles  of  a  cell  or  other 
points  of  different  potential  be  joined  by  a  well- 
drawn  wire,  the  potential  through  the  wire  will 
fall  uniformly  from  the  anode  to  the  cathode. 
The  greater  the  resistance  in  the  wire,  the  more 
uniform  will  be  the  fall  in  potential.  The  rheo- 
cord (Fig.  5)  consists  of  10  metres  of  thin  well- 
drawn  German  silver  wire  (No.  30).  Binding  posts 
are  placed  at  the  beginning  of  the  continuous  wire, 
one  metre  from  the  beginning,  and  at  the  end. 


Fig.  5.  The  rheocord.  A  metre  rule  is  screwed  to  the  lid  of  a  shallow 
box  of  oak.  At  each  end  is  a  binding  post.  To  the  post  marked  0  is 
fastened  one  end  of  an  unbroken  German  silver  wire  (No.  30)  ten  metres  in 
length.  This  wire  passes  over  the  metre  stick  to  post  1,  and  thence  into 
the  box,  where  the  remaining  nine  metres  go  to  and  fro  between  two  rows  of 
pegs  at  the  ends  of  the  under  side  of  the  cover  of  the  box.  The  end  of  the 
10  metre  wire  is  brought  out  of  the  box  and  fastened  to  post  10. 

The  resistance  in  the  10  metres  of  thin  Ger- 
man silver  wire  is  so  great  (about  64  ohms)  that 
the  internal  resistance  of  the  element  furnishing 
the  electromotive  force,  together  with  the  resist- 
ance of  the  large  copper  connecting  wires,  prac- 
tically disappears  for  such  measurements  as  we 
shall  need  to  make.  As  the  fall  of  potential  is 
uniform  throughout  the  10  metres,  the  difference 
of  potential  between  post  0  and  post  1  will  be 
practically  one-tenth   the  electromotive  force  of 


METHODS   OF    ELECTRICAL   STIMULATION        21 

the  element.  Thus  when  the  sliding  contact  is 
at  post  1,  the  capillary  electrometer  receives  one- 
tenth  the  electromotive  force  of  the  element.  By 
moving  the  slider  from  post  1  towards  post  0, 
any  desired  fraction  of  this  one-tenth  may  be 
measured  by  the  electrometer.1 

The  Cell.  —  In  CJalvani's  experiment,  the  con- 
tact of  two  dissimilar  metals  with  the  saline 
fluids  of  animal  tissue  caused  a  movement  of 
ions  and  a  difference  of  potential.  The  action 
may  be  studied  more  conveniently  when  the 
liquid  is  placed  in  a  cell. 

Connect  a  platinum  and  a  zinc2  plate  through 

1  The  electrometer  should  always  be  used  in  short  circuit, 
so  that  the  capillary  and  the  mercury  in  the  reservoir  shall 
always  be  connected  through  a  conductor.  The  short  circuit 
may  be  provided  through  a  key  or  through  the  rheocord  (Fig.  6, 
page  22).  Perhaps  the  most  convenient  arrangement  is  that 
shown  in  Fig.  4,  in  which  a  strip  of  spring  brass  connected  with 
one  of  the  binding  posts  of  the  electrometer  rests  against  a 
second  piece  of  brass  connected  with  the  other  binding  post 
except  when  depressed  by  the  finger.  The  point  of  higher 
potential,  when  known,  should  always  be  connected  with  the 
capillary.  The  zinc  is  that  point  in  the  ordinary  zinc-carbon 
or  zinc-platinum  element.  The  student  is  reminded  that  in 
the  circuit  outside  the  element,  the  potential  falls  from  the 
carbon  to  the  zinc. 

2  It  will  be  observed  that  the  zinc  is  amalgamated.  Chemi- 
cally pure  zinc  does  not  need  amalgamation.  Commercial  zinc 
contains  iron,  arsenic,  etc.,  as  impurities.  The  contact  of  una- 
malgamated  zinc  and  these  dissimilar  metals  with  an  electrolyte 
creates  a  difference  of  potential,  and  parasitic  currents  run  from 


22   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

a  simple  key  with  posts  0  and  10  of  the  rheocord 
as  shown  in  Fig.  6.  Connect  the  zero  post  and 
the  slider  with  the  capillary  electrometer  through 
a  short-circuiting  key. 

Bring  the  capillary  into  the  field  of  the  micro- 
scope (Leitz  objective  3,  micrometer  ocular), 
parallel  to  the  micrometer  scale.  The  end  of  the 
tube  should  be  just  visible  at 
the  upper  margin  of  the  field. 
If  the  meniscus  is  not  visible, 
turn  the  pressure  screw  slowly 
to  the  right  until  the  meniscus 

enters  the  field.     Note  the  posi- 
ng. 6.  .  x 

tion  of  the  meniscus  on  the 
scale.  Close  the  battery  key.  Let  an  assistant 
place  the  metals  in  a  beaker  containing  solution 
of  sodium  chloride.  Open  the  short-circuiting 
key  of  the  electrometer. 

the  zinc  to  the  foreign  metals.  These  currents  are  prevented  hy 
covering  the  impurities  with  zinc  amalgam,  the  electromotive  prop- 
erties of  which,  toward  sulphuric  acid,  are  those  of  pure  zinc. 
As  the  zinc  in  the  amalgam  dissolves  out,  the  film  of  mercury 
unites  with  fresh  zinc.  Zinc  is  amalgamated  best  by  adding 
4  per  cent  of  mercury  to  the  molten  zinc  before  casting;  or  the 
zinc  may  be  dipped  in  10  per  cent  sulphuric  acid  to  clean  it, 
and  mercury  rubbed  over  the  surface  with  a  brush  or  a  stick 
padded  with  cloth ;  or  the  zinc  may  be  dipped  in  a  solution 
from  which  the  mercury  will  deposit  on  the  zinc.  Formula  for 
amalgamating  fluid  :  warm  gently  4  parts  mercury  in  5  parts 
concentrated  nitric  acid  and  15  parts  concentrated  hydrochloric 
acid  irntil  dissolved,  and  then  add  20  parts  more  of  concen- 
trated hydrochloric  acid. 


METHODS   OF  ELECTRICAL   STIMULATION        23 

"When  the  metals  touch  the  electrolyte  a  dif- 
ference in  potential  will  be  set  up,  and  the 
meniscus  will  move  in  the  capillary. 

Nute  the  number  of  divisions  of  the  scale 
traversed  by  the  meniscus.  Open  the  key.  Wait 
several  minutes. 

Now  bring  the  meniscus  back  to  its  original 
position  on  the  scale.     Close  the  key. 

The  meniscus  will  move  to  a  much  slighter 
extent  than  when  the  circuit  was  first  made. 

As  the  displacement  of  the  meniscus  is  propor- 
tional to  the  electromotive  force  of  the  cell,  it  is 
obvious  that  the  latter  has  rapidly  diminished. 
The  solution  contains  the  ions  of  water  as  well 
as  those  of  the  salt.  When  the  circuit  between 
the  platinum  and  zinc  is  completed  the  cations 
H+  and  Xa+  move  towards  the  cathode.  There 
the  more  easily  de-ionized  H+  yields  up  its  elec- 
tricity and  hydrogen  appears  on  the  cathode. 
The  corresponding  quantity  of  electricity  is  con- 
veyed into  the  solution  at  the  anode  by  ioniza- 
tion of  the  zinc.  The  deposition  of  hydrogen 
on  the  negative  plate  checks  the  electromotive 
force  setting  from  the  zinc  to  the  platinum  in 
two  ways :  first,  because  gas  is  a  bad  conductor, 
and  the  effective  surface  of  the  platinum  is 
thereby  diminished  by  the  bubbles  collecting 
on  it;  and  secondly,  because  hydrogen  is  electro- 
positive, ami   creates   an   electromotive   force    in 


24      THE   PHYSIOLOGY   OF   MUSCLE    AND   NERVE 

the  direction  from  platinum  to  zinc,  and  thus 
"  polarizes "  the  cell.  This  new  electromotive 
force  opposes  the  original  current  from  zinc  to 
platinum. 

The  Daniell  Cell.  —  Daniell  discovered  an  elec- 
tro-chemical method  of  avoiding  polarization,  and 
thus  was  able  to  construct  a  cell  that  would 
furnish  a  current  of  unvarying  strength.  In  the 
Daniell  cell  the  two  metals  employed  are  zinc 
and  copper.  The  amalgamated  zinc  is  placed  in 
a  porous  cup  filled  with  dilute  sulphuric  acid. 
The  copper  is  placed  in  a  solution  of  copper  sul- 
phate kept  saturated  by  crystals  of  the  salt. 
When  the  circuit  is  closed,  the  zinc  "  dissolves  "  in 
the  sulphuric  acid,  carrying  with  it  the  elec- 
tricity with  which  the  zinc  ions  are  charged. 
The  electricity  is  carried  through  the  solution 
by  the  migration  first  of  hydrogen  and  then  of 
copper  ions.  It  leaves  the  solution  at  the  cath- 
ode where  the  copper  ions  are  converted  into 
metallic  copper  and  deposited  on  the  cathode. 
The  quantity  of  zinc  dissolved  and  copper  de- 
posited is  proportional  to  the  quantity  of  the 
current.  One  ampere  deposits  per  minute  19.75 
milligrams  copper,  and  dissolves  20.32  milligrams 
zinc. 

It  is  to  be  observed  that  each  metal  is  placed 
in  a  solution  of  its  own  salt.    The  ions  carried  to 


METHODS   OF    ELECTRICAL    STIMULATION        25 

the    respective   poles    are    of   the   same   nature 
chemically  as  the  poles  themselves,  and  hence  do 


Pig.  7  A. 


Fig.  7  I!. 


A,  the  pole-changer;  B,  diagram  <'f  pole-changer  arranged  (l)to  change 
the  direction  of  tin-  current,  (2)  as  a  double  key,  without  cross-wires,  (3)  as 
a  simple  key. 

not  set  up  opposing  electromotive  forces  when 
they  are  de-ionized. 

The  current  produced  by  the  Daniell  cell  is 
almost  perfectly  constant, 
so  long  as  sulphuric  acid 
still  remains  uncombined, 
and  so  long  as  the  sul- 
phate of  copper  solution 
is  kept  saturated. 

It  may  he  remarked 
that  the  function  of  the 
porous  cup  is  to  keep  the 
copper  from  depositing  on  the  zinc. 

Polarization    Current.  —  Place    two     pieces     of 

platinum  foil  in  a  solution  of  copper  sulphate, 
and  connect   them   to   a   pole-changer  (without 


Fig.  8. 


26   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

cross-wires).  Connect  the  remaining  pairs  of 
posts  with  two  dry  cells  in  series  (carbon  of  one 
cell  connected  with  zinc  of  other),  and  with  the 
0  and  1  metre  posts  of  the  rheocord,  respectively. 
Connect  the  zero  post  and  the  slider  to  the  capil- 
lary electrometer  (Fig.  8).  Turn  the  pole-changer 
to  pass  the  battery  current  through  the  copper 
sulphate  solution  or  "electrolyte."  The  cation 
(copper)  will  be  partially  de-ionized  at  the  nega- 
tive pole,  or  cathode,  on  which  copper  will  be  de- 
posited in  a  fine  film.  The  anion  (sulphion,  S04) 
will  pass  towards  the  positive  pole,  or  anode. 
Since,  however,  the  traces  of  oxygen  ions  present 
in  the  water  are  more  easily  de-ionized  than  the 
S04  group,  oxygen  will  appear  at  the  anode  and 
the  S04  ions  will  remain  in  the  solution. 

The  elements  copper  and  oxygen  deposited 
respectively  on  the  cathode  and  anode  tend  to 
fly  back  into  the  ionic  state  ;  and  this  tendency, 
taken  in  connection  with  the  opposing  osmotic 
force  of  the  ions  already  in  solution,  sets  up 
an  electromotive  force  equal  to  that  which  caused 
the  de-ionization,  but  in  an  opposite  direction. 
Hence  the  polarization  current.  On  cutting  off 
the  electrolyzing  current,  the  polarization  current 
may  be  measured. 

Note  the  position  of  the  meniscus  of  the  capil- 
lary electrometer.    Turn  the  pole-changer  so  that 


METHODS    OF   ELECTRICAL    STIMULATION        27 

the  cell  is  cut  off  and  the  electrodes  brought  into 
the  electrometer  circuit. 

The,  meniscus  will  indicate  a  current  opposite  in 
direction  to  the  current  from  the  cell. 

Electrolysis  of  Potassium  Iodide  —  An  interest- 
ing example  of  electrolysis  is  seen  in  the  decom- 
position of  potassium  iodide. 

Dip  a  small  piece  of  filter  paper  in  starch  paste 
to  which  a  little  potassium  iodide  has  been  added, 
and  lay  the  paper  over  the  platinum  electrodes. 
Make  the  circuit. 

A  dark  blue  color  appears  at  the  anode.  Iodine 
is  set  free  at  the  anode  and  forms  iodide  of  starch. 
This  method  may  be  used  to  determine  which 
pole  is  the  anode.  The  direction  of  the  current 
in  the  secondary  coil  of  the  inductorium  may  be 
thus  recognized. 

Dry  Cell.  — A  "  dry  "  cell  is  very  convenient  for 
large  classes.  It  usually  consists  of  a  zinc  cup, 
lined  with  plaster  of  Paris,  saturated  with  am- 
monium chloride,  in  the  centre  of  which  is  a 
carbon  plate  surrounded  with  black  oxide  of 
manganese.  AVhen  the  cell  is  in  action,  the  zinc 
forms  a  double  chloride  of  zinc  and  ammonium, 
while  ammonia  gas  and  hydrogen  are  liberated  at 
the  carbon  pole.  These  cells  should  never  be 
used  continuously  for  many  minutes,  for  they  are 
rapidly  polarized  by  the  accumulation  of  hydro- 


28      THE    PHYSIOLOGY    OF   MUSCLE    AND   NERVE 

gen  on  the  carbon  plate.  The  unused  cell  regains 
its  difference  of  potential  by  the  union  of  the 
hydrogen  with  the  oxygen  slowly  given  off  by 
the  manganese  dioxide,  which  therefore  acts  as  a 
depolarizer. 

Graduation  of  the  Electrometer.  —  It  already 
has  been  stated  that  the  pressure  necessary  to 
bring  back  the  meniscus  of  the  capillary  electrom- 
eter to  its  original  position  is  proportional  to 
the  electromotive  force  that  displaced  the  men- 
iscus. Thus  if  the  electrometer  is  connected  with 
a  known  difference  of  potential,  for  example,  the 
poles  of  a  Daniell  cell,  the  potential  of  which  is 
1.1  volt,  the  meniscus  will  be  so  far  displaced  that 
a  pressure  of  30  mm.  of  mercury  may  be  necessary 
to  restore  it  to  its  original  position  on  the  microm- 
eter scale.  In  that  case,  a  displacement  compen- 
sated by  a  pressure  of  3  mm.  Hg  would  indicate 
a  difference  of  potential  of  ^  of  1.1  volts,  or  0.11 
volt ;  1  mm.  Hg  pressure  would  compensate  gY0 
volt,  and  so  on,  —  the  relation  between  pressure 
and  difference  of  potential  is  a  simple  linear  one. 
But  this  is  true  only  when  the  capillary  is  of 
equal  calibre  throughout  the  region  traversed  by 
the  meniscus.  The  shorter  this  region,  the  more 
likely  is  the  calibre  to  be  uniform.  Uniformity 
is  also  greater  near  the  end  of  the  capillary  than 
near  the   tube    from   which   it   is   drawn.     The 


METHODS  OK   ELECTRICAL   STIMULATION       29 

electromotive  forces  to  be  measured  in  physio- 
logical experimentation  are  usually  very  slight. 
It  is  of  advantage  therefore  always  to  bring  tbe 
meniscus  near  tbe  end  of  tbe  capillary,  and  to 
connect  tbe  positive  element  (zinc)  with  tbe  cap- 
illary mercury.  Tbe  meniscus  will  thus  always 
traverse  tbe  same  most  uniform  part  of  tbe  cap- 
illary in  tbe  same  direction.  By  limiting  tbe 
graduation  to  tins  portion,  tbe  error  incident  to 
inequalities  of  bore  will  be  much  less.  One- 
twentietb  tbe  voltage  of  a  Daniell  cell  will  cause 
a  sufficient  displacement  of  tbe  meniscus. 

To  graduate  tbe  electrometer,  tbe  connections 
should  be  made  as  in  Fig.  G.  Tbe  short-circuit- 
ing key  should  be  closed.  Tbe  slider  should  be 
50  cm.  from  tbe  positive  post.  Take  care  that 
tbe  zinc  is  connected  with  the  capillary  mercury. 
Bring  the  meniscus  into  tbe  lower  part  of  tbe  field. 
Note  its  position  on  the  micrometer  scale.  Note 
the  level  of  tbe  mercury  in  tbe  manometer.  Open 
the  key.  The  meniscus  will  retreat  in  the  cap- 
illary. Eaise  tbe  pressure  until  tbe  meniscus 
returns  to  its  former  position.  Read  tbe  manom- 
eter again.  Lower  tbe  pressure  in  tbe  manometer. 
Close  the  key.  Tbe  difference  between  tbe  two 
manometer  readings  is  tbe  pressure  in  millimetres 
of  mercury  necessary  to  compensate  an  electro- 
motive force  of  0.055  volt.     Divide  0.055  by  tbe 


30      THE    PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

number   of   millimetres.      The    quotient   is   the 
electromotive  force  for  one  millimetre  pressure.1 

Advantages  of  the  Electrometer.  —  The  mass  of 
mercury  displaced  in  the  movement  of  the  menis- 
cus is  very  small,  and  the  distance  through  which 
it  is  moved  is  short.  Hence  the  inertia  of  posi- 
tion is  easily  overcome  and  the  inertia  of  motion 
(which  is  proportionate  to  the  mass  times  the 
square  of  the  velocity)  is  practically  wanting. 
The  absence  of  inertia  errors,  the  almost  instan- 
taneous quickness  with  which  the  meniscus  takes 
its  new  position,  the  ease  with  which  slight  elec- 
tromotive forces  (To  o  o"o  v°lt)  may  be  measured, 
and  simplicity  of  construction,  are  the  principal 
advantages  of  this  admirable  instrument. 

Induction  Currents 

A  most  useful  method  of  electrical  stimulation 
of  living  tissues  is  by  the  induced  current,  and  a 
clear  idea  of  the  phenomena  of  induction  must 
now  be  gained. 

Magnetic  Induction.  —  Faraday's  experiment. 
Remove  the  secondary  (larger)  coil  of  the  induc- 

1  In  practice,  the  relation  between  the  pressure  and  the  poten- 
tial must  frequently  be  re-determined.  For  most  purposes,  it  is 
better  to  measure  differences  of  potential  by  compensation  as 
explained  on  page  158.  The  electrometer  then  serves  to  show  the 
point  at  which  compensation  is  reached. 


METHODS   OF   ELECTRICAL   STIMULATION        31 

toriuni  (Fig.  9)  from  its  slideway  and  connect 
its  terminals  with  the  capillary  electrometer. 
Raise  the  brass  bridge  between  the  binding 
posts.  (If  this  bridge  is  down  its  thick 
metallic  mass   will  offer  such  an  easy  path  be- 


Fig.  9.  The  indnctorium,  simple  key,  and  platinum  electrodes.  The  in- 
ductorium  is  arranged  for  single  induction  currents  ;  when  the  battery 
wires  are  placed  in  binding  posts  2  and  3,  the  primary  current  will  pass 
through  the  automatic  interrupter  and  a  continuous  series  of  make  ami 
break  induction  currents  will  be  secured.  The  secondary  coil  is  turned 
upon  its  pivot.  The  ends  of  the  secondary  wire  are  fastened  to  two  posts 
which  may  be  connected  by  the  brass  bridge,  in  which  case  the  induced 
currents  are  short-circuited. 

One  of  the  posts  on  the  simple  key  is  connected  to  a  reservoir  of  mercury, 
the  other  to  a  Bpring  brass  strip.  The  litter  bears  at  its  free  end  an  iron 
wire  that  makes  contact  with  the  mercury  when  the  wire  is  pressed  down 
through  a  short  hard  rubber  tube  (t"  prevenl  spilling  the  mercury)  fastened 
about  a  small  hole  in  the  hard  rubber  cover  of  the  reservoir.  The  wire 
may  be  held  in  this  position,  as  in  the  figure,  by  pushing  a  pivoted  brass 
fastener  over  the  strip  which  bears  the  wire. 

tween  the  ends  of  the  secondary  wire  that  nearly 
all  —  practically  all  —  the  electricity  produced 
in  this  coil  will  pass  over  the  bridge,  instead  of 
by  the  relatively  1  ong,  thin  wires  leading  to  the 
electrometer.)    Bring  the  meniscus  into  the  field. 


32      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

Thrust  the  north  pole  of  a  magnetized  rod  within 
the  coil. 

The  meniscus  will  move,  indicating  that  an 
electric  current  has  been  induced  in  the  second- 
ary coil.     Note  the  direction  of  the  current. 

Let  the  magnet  remain  in  the  coil. 

The  meniscus  will  return  to  its  former  posi- 
tion. Evidently  the  induced  current  is  of 
momentary  duration. 

"Withdraw  the  magnet  quickly. 

The  meniscus  will  move  in  the  opposite 
direction. 

Insert  the  south  pole. 

The  induced  current  now  has  the  direction 
opposite  to  that  of  the  current  induced  by  the 
insertion  of  the  north  pole. 

Withdraw  the  magnet  quickly. 

The  induced  current  has  the  direction  opposite 
to  that  of  the  current  induced  by  the  withdrawal 
of  the  north  pole. 

These  results  may  be  thus  expressed :  the 
moving  of  a  magnet  in  the  neighborhood  of  a 
conductor,  or  of  a  conductor  in  the  neighbor- 
hood of  a  magnet,  produces  in  the  conductor  an 
electromotive  force,  which,  on  the  circuit  being 
completed,  creates  a  current  that  would  impart 
to  the  magnet  or  the  conductor  a  movement  in 
the  opposite  direction. 


METHODS   OF   ELECTRICAL   STIMULATION 

Magnetic  Field.  Lines  of  Force.  —  The  space 
about  a  magnet  in  which  the  magnetic  forces 
act  is  called  the  "  field  "  of  the  magnet.  If  very 
fine  iron  tilings  are  dusted  through  a  muslin 
cloth  onto  a  thin  card  perforated  near  the  centre  by 
a  copper  wire  or  other  conductor,  and  a  strong  cur- 
rent is  passed  through  the  wire,  the  filings  will  ar- 
range themselves  in  concentric  circles  around  the 
wire,  particularly  if  the  card  be  gently  tapped. 

The  position  of  these  "  lines  of  force  "  shows 
the  direction  of  the  magnetic  force,  and  their 
number  is  an  index  of  its  intensity. 

To  produce  Electric  Induction,  the  Lines  of  Mag- 
netic Force  must  be  cut  by  the  Circuit.  —  Hold  the 
magnet  at  right  angles  to  the  axis  of  the  coil, 
and,  keeping  it  in  this  position,  rapidly  advance 
it  towards  the  coil. 

The  electrometer  will  show  no  current,  be- 
cause the  number  of  the  lines  of  magnetic 
force  which  pass  through  the  field  of  the  con- 
ductor has  not  been  altered. 

Electromagnetic  Induction.  —  An  electromagnet 
may  be  used  in  place  of  the  bar  magnet  to  pro- 
duce induction. 

Connect  a  dry  cell  through  a  simple  key  with 
posts  1  and  2  of  the  primary  coil.    Close  the  key. 

When  the  current  passes  through  the  primary 
coil,  the  core  of  iron  wire  in  the  coil  will  be 
3 


34      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

magnetized,  as  is  shown  by  its  attracting  the 
head  of  the  Wagner  hammer. 

Bring  the  meniscus  into  the  field.  Approach  the 
primary  coil  to  the  secondary  as  in  the  experiment 
with  the  magnet.     Withdraw  the  primary  coil. 

The  electrometer  shows  the  presence  of  in- 
duced currents,  as  before.  These  currents  are 
momentary.  The  first  induction  current  is  in- 
verse, *'.  e.  it  runs  round  the  secondary  coil  in  the 
direction  opposite  to  that  taken  by  the  battery  cur- 
rent in  the  primary  coil.  The  second  induced  cur- 
rent is  in  the  same  direction  as  the  primary  current. 

Place  the  coils  at  right  angles  to  each  other. 
Approach  one  towards  the  other. 

No  current  will  be  induced. 

Make  and  break  Induction.  —  Close  and  open 
the  key  in  the  primary  circuit,  thus  making  and 
breaking  the  primary  current. 

The  effect  is  the  same  as  if  the  primary  were 
suddenly  brought  up  to  the  secondary  coil  from 
an  infinite  distance  and  removed  again.  The  make 
induction  current  is  in  the  opposite,  the  break  in 
the  same,  direction  as  the  primary  current. 

Turn  the  secondary  coil  on  its  pivot  until  the 
axis  is  at  right  angles  to  the  axis  of  the  primary 
coil.     Make  and  break  the  primary  current. 

No  induction  will  take  place  provided  the 
angle  between  the  coils  is  precisely  90°. 


METHODS   OF   ELECTRICAL   STIMULATION        35 

The  inductorium.  —  Examine  the  construction 
of  the  inductorium.  The  primary  coil  consists 
of  a  few  turns  of  thick  wire.  More  turns  would 
increase  resistance  and  self-induction,  —  the 
counter  induction  set  up  in  each  turn  of  the 
primary  wire  by  the  passage  of  the  primary 
current    through    neighboring    turns,  —  without 

o  o  o 

increasing  the  induction  effect  in  the  secondary 
coil. 

The  iron  core  adds  to  the  number  of  lines  of 
magnetic  induction  which  pass  through  the  coils. 
It  has  been  already  shown  (page  33)  that  the 
lines  of  magnetic  induction  produced  by  the  pas- 
sage of  an  electric  current  through  a  wire  are 
closed  circles.  If  the  centre  of  the  coil  were 
filled  with  air,  most  of  these  circles  would  remain 
closed  about  their  own  wire,  for  air  is  not  readily 
permeable  to  magnetism.  But  when  the  iron  core 
is  placed  within  the  coil  the  greater  part  of  the 
magnetic  induction  follows  the  iron  (because  it 
is  more  permeable)  from  end  to  end  of  the  core, 
returning  outside  through  the  air.  Thus  the 
number  of  effective  lines  is  increased.  A  bundle 
of  iron  wires  is  used  instead  of  a  solid  core,  be- 
cause no  induced  current  is  then  possible  through 
the  mass  of  the  iron,  as  would  be  the  case  in  a 
solid  core.  Such  a  current  would  slow  the  speed 
of  magnetization  and  demagnetization. 


36      THE   PHYSIOLOGY    OF   MUSCLE   AND   NERVE 

The  secondary  coil  is  made  of  many  turns  of 
fine  wire,  because  the  object  of  the  inductorium 
is  to  transform  the  low  electromotive  force  of  the 
cell  into  the  high  electromotive  force  of  the  in- 
duced current.  In  the  induction  coil,  as  in  other 
transformers,  the  electromotive  forces  in  the 
primary  circuit  are  to  those  produced  in  the 
secondary  circuit  approximately  as  the  number 
of  turns  of  wire  in  the  primary  is  to  the  number 
in  the  secondary  circuit. 

If  the  induced  current  is  to  be  passed  through 
conductors  of  low  resistance,  the  high  internal 
resistance  of  the  secondary  coil,  due  to  its  great 
length  of  fine  wire,  will  be  of  importance. 

Place  a  dry  cell  with  simple  key  in  the  pri- 
mary circuit  of  an  inductorium  (posts  1  and  2). 
Connect  the  secondary  coil  with  a  galvanometer. 
Note  the  excursion  of  the  needle  with  a  break 
induction  current.  Replace  the  secondary  coil 
with  one  of  fewer  windings  (the  primary  coil  of 
a  second  inductorium  will  serve).  Let  the  dis- 
tance between  primary  and  secondary  coil  be  the 
same  as  before. 

The  excursion  of  the  needle  with  a  break  in- 
duction current  will  be  increased,  or  at  least  not 
proportionately  diminished. 

If,  on  the  other  hand,  the  induced  current  is 
to  be  passed  through  nerve,  muscle,  or  skin.  the. 


METHODS    OF   ELECTRICAL   STIMULATION        37 

resistance  of  the  secondary  coil  will  practically 
be  nothing  in  comparison  with  the  enormous 
resistance  of  animal  tissue. 

Repeat  the  preceding  experiment,  introducing 
in  the  secondary  circuit  a  high  external  resist- 
ance, i.  e.  a  nerve. 

The  secondary  coil  with  many  turns  of  fine  wire 
now  causes  a  much  greater  deflection  of  the  gal- 
vanometer needle  than  the  coil  with  fewer  turns. 

Interrupter.  —  Instead  of  making  and  break- 
ing the  primary  circuit  by  hand,  an  automatic 
interrupter  is  provided.  The  primary  circuit 
passes  through  a  screw,  the  point  of  which  con- 
veys the  current  through  a  flat  spring  upon 
which  is  mounted  an  iron  disk  opposite  and  near 
to  the  core  of  wire  in  the  primary  coil.  When 
the  current  enters  the  primary  coil,  the  core  is 
magnetized  and  draws  upon  the  iron  disk.  The 
spring,  to  which  the  disk  is  attached,  is  thereby 
drawn  away  from  the  screw-point  through  which 
the  current  is  passing.  Thus  the  current  is 
broken,  and  ceases  to  flow  through  the  primary 
coil;  the  core  no  longer  is  magnetized,  and  re- 
leases  the  iron  disk;  the  spring  again  makes 
contact  with  the  screw-point,  the  current  is  re- 
established, only  to  be  at  once  again  broken. 
Thus  a  rapid  series  of  make  and  break  induc- 
tion currents  is  secured. 


38      THE    PHYSIOLOGY    OF   MUSCLE   AND   NERVE 

Draw  a  diagram  of  the  primary  circuit,  indi- 
cating the  connections  of  the  inductorium. 

Empirical  Graduation  of  Inductorium.  —  Con- 
nect the  secondary  coil  with  the  galvanometer. 
Join  the  primary  coil  to  a  dry  cell,  interposing  a 
simple  key.  Turn  the  secondary  coil  on  its  pivot 
until  it  is  at  right  angles  with  the  primary  coil. 
Close  the  circuit. 

The  galvanometer  needle  will  not  swing. 
There  is  no  induced  current.1 

Turn  the  secondary  coil  on  its  pivot,  closing 
the  key  from  time  to  time  to  test  the  induction. 

The  strength  of  the  induction  increases  ap- 
proximately as  the  cosine  of  the  angle  between 
the  coils  increases.  An  empirical  graduation  is 
sometimes  placed  on  a  circular  scale  beneath  the 
coil. 

When  the  axes  of  the  two  coils  lie  in  the  same 
plane,  slide  the  secondary  towards  the  primary, 
making  and  breaking  the  primary  current  from 
time  to  time. 

The  potential  of  the  primary  upon  the  second- 
ary coil,  i.  e.  the  sum  of  the  inductions  of  each 
element  of  the  primary  upon  all  the  elements  of 
the  secondary  coil,  increases  as  the  secondary  is 
brought  nearer  the  primary  coil.  The  increase  is 
not  linear.     As  the  distance  between  the  coils 

1  It  is  difficult  to  place  the  coil  precisely  at  an  angle  of  90.° 


METHODS   OF    ELKCTKICAL   STIMULATION        39 

diminishes,  the  increment  of  increase  in  the  in- 
tensity of  the  induced  current  is  not  the  same 
but  greater  for  each  centimetre  of  approach. 

Graduation.  —  Fasten  a  strip  of  white  gummed 
paper  at  the  side  of  the  base  of  the  inductorium, 
beginning  at  the  end  block  which  holds  the 
primary  coil.  Place  the  secondary  coil  at  the 
end  of  the  slideway.  Make  the  primary  current. 
Read  the  number  of  degrees  of  deviation  for  the 
break  induction  current  only.  Make  a  line  on 
the  paper  band  exactly  opposite  that  end  of  the 
secondary  coil  which  is  nearer  the  primary. 
When  the  needle  is  again  at  rest,  move  the 
secondary  nearer  the  primary  coil,  and  find  the 
distance  at  which  the  deviation  of  the  needle  in 
response  to  the  break  induction  current  is  n  de- 
grees (for  example,  two)  of  the  scale  larger  than  at 
the  former  position  of  the  coil.  Mark  on  the  white 
strip  the  new  position  of  the  coil.  Continue  in 
this  way  to  find  the  positions  of  the  secondary 
coil  at  which  the  needle  shows  successively  a 
deviation  two  degrees  greater  at  each  new  posi- 
tion, and  mark  them  on  the  paper  band. 

The  marks  on  this  empirical  scale  will  be 
nearer  together  as  the  secondary  approaches  the 
primary  coil.1 

1  The  rough  method  here  employed  serves  merely  to  show 
that  the  increase  in  the  intensity  of  the  induction  current  as 


40      THE    PHYSIOLOGY   OF  MUSCLE   AND   NEKVE 

Make  and  Break  Induction  Currents  as  Stimuli. 

—  Make  a  nerve-muscle  preparation.  Connect  a 
dry  cell  with  simple  key  to  the  primary  coil 
(posts  1  and  2).  Fasten  in  the  posts  of  the 
secondary  coil  the  stimulation  electrodes,  i.  e. 
the  prolongation  of  the  ends  of  the  secondary 
wire  which  convenience  demands.  .  Put  the 
secondary  coil  at  the  end  of  the  slideway.  Place 
the  electrode  points  against  the  nerve.  Open 
and  close  the  primary  circuit. 

The  muscle  does  not  contract. 

Move  the  secondary  towards  the  primary  coil, 
opening  and  closing  the  primary  circuit. 

Presently  the  threshold  value  will  be  reached 
and  the  muscle  will  shorten.  Observe  that  this 
contraction  was  the  result  of  a  break  induction 
current,  not  a  make. 

Cautiously  move  the  secondary  coil  still  nearer 
the  primary,  making  and  breaking  the  current  as 
before. 

A  point  will  be  reached  at  which  the  make 
induction  also  causes  contraction.  Obviously, 
the  break  current  is  a  stronger  stimulus  than 
the  make  induction  current.  Tbe  cause  of  the 
greater  intensity  of  the  break  induction  current 
lies  in  the  primary  coil.     The  current  which  en- 

the  coils  approach  is  not  linear.  An  exact  method  of  gradua- 
tion has  been  given  by  Kronecker. 


METHODS    OF   ELECTRICAL    STIMULATION        41 

ters  the  primary  coil  induces  a  current  in  this 
coil  as  well  as  in  the  secondary  coil.  The  direc- 
tion of  this  "self-induced"  current  is  opposite  to 
that  of  the  primary  current,  and  hence  weakens 
it  and  delays  its  development.  The  stimulating 
power  of  electricity  increases  with  both  the  inten- 
sity of  the  current  and  the  quickness  with  which 
the  intensity  alters.  Hence  the  stimulating  power 
of  the  make  induction  current  is  lessened  by  the 
self-induction  of  the  primary  coil.  When,  on 
the  other  hand,  the  primary  circuit  is  broken, 
the  current  stops,  and  although  self-induction 
again  takes  place,  it  cannot  affect  the  primary 
current,  because  the  latter  no  longer  exists.  The 
self-induced  current  at  the  break  of  the  primary 
current  is  in  the  same  direction  as  the  primary 
current. 

The  Extra  Currents  at  the  Opening  and  Closing  of 
the  Primary  Current.  —  1.  Remove  the  secondary 
coil  from  the  inductorium.  Connect  posts  1  and 
2  of  the  primary  coil  with  a  dry  cell,  interposing 
a  simple  key.  Fasten  the  ends  of  the  electrode 
wires  in  these  same  posts.  Close  the  primary 
circuit.  Place  the  electrode  points  against  the 
tongue.     Open  the  key. 

A  shock  from  the  self-induced  current  devel- 
oped in  the  primary  coil  will  be  felt 

Draw  a  diagram  of  the  circuits, 


42   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

2.  Connect  a  dry  cell  through  a  key  to  the 
metre  posts  of  the  rheocord  (Fig.  10).  •  Connect 
the  positive  post  and  the  slider  to  the  primary 
coil  of  an  inductorium  arranged  for  single  induc- 
tion currents.  Bring  wires  from  these  posts  of 
the  primary  coil  through  a  simple  key  to  the 
nerve  of  a  nerve-muscle  preparation.  Close  the 
key   in    the    primary    circuit.     Open    and   close 

the  key  in  the  nerve  circuit. 
E=>=       The    muscle  will   contract   at 

closure  and  possibly  at  open- 


2 


,  cpp  N>  ing.     By  means  of  the  slider, 

\  /  weaken   the    current   through 

*    '--  6      -^>f)       the  primary  coil  until  opening 
V_^  /       and    closing    the   key    to   the 

^<>y  nerve  no  longer  produces  con- 

traction.     Now   let   this   key 

Fig.  10.  • 

remain  closed  and  make  and 
break  the  primary  circuit. 

The  muscle  will  contract  both  on  opening  and 
closure.  The  induction  currents  developed  in 
the  primary  coil  when  the  primary  current  is 
made  and  broken  stimulate  the  nerve,  al- 
though the  galvanic  current  itself  is  powerless 
to  do  so. 

Tetanizing  Currents.  —  Connect  a  dry  cell  to 
posts  2  and  3  of  the  primary  coil.  The  vibrat- 
ing riammer  will  automatically  make  and  break 


METHODS   OF    BLECTEIOAL   STIMULATION         43 

the  current.  Place  the  electrodes  against  the 
nerve  or   muscle. 

The  muscle  will  contract  once  for  each  induc- 
tion current,  but  the  contractions  are  so  rapid 
that  they  fuse  into  a  prolonged  shortening 
termed  tetanus. 

Induction  in  Nerves.  —  Faraday  discovered  that 
currents  can  be  induced  in  electrolytes  as  well 
as  metallic  conductors.  Induced  currents  may 
therefore  appear  in  nerves  lying  sufficiently  near 
a  primary  circuit. 

Lay  the  well-moistened  nerve  of  a  nerve-muscle 
preparation  around  the  primary  coil  protected  by 
a  piece  of  paraffin  paper  in  such  a  way  that  the 
free  end  of  the  nerve  touches  the  nerve  near  the 
muscle  or  touches  the  muscle  itself,  so  as  to  form 
a  closed  circuit.  Make  and  break  the  primary 
current. 

Make  and  break  currents  will  be  induced  in 
the  nerve,  and  the  muscle  will  contract. 

Exclusion  of  Make  or  Break  Current.  —  Con- 
nect the  dry  cell  with  posts  1  and  2,  interposing 
a  key.  See  that  the  short-circuiting  key,  i.  e.  the 
thick  brass  bridge  In 'tween  the  posts  on  the  sec- 
ondary coil,  is  down.  Connect  the  electrodes 
with  the  secondary  coil,  and  place  their  points 
against  the  nerve  of  a  nerve-muscle  preparation. 
Close  the  primary  key. 

The  muscle  will  not  contract. 


44   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

The  resistance  to  the  passage  of  the  induced 
current  through  the  portion  of  nerve  between 
the  ends  of  the  electrodes  is  many  thousand 
times  greater  than  the  resistance  of  the  brass 
bridge  or  short-circuiting  key.  Practically  none 
of  the  electricity  will  pass  through  the  nerve 
when  the  short-circuiting  key  is  closed. 

Open  the  short-circuiting  key  and  then  open 
the  primary  key. 

The  muscle  contracts. 

Eepeat  the  experiment,  letting  the  make  cur- 
rent pass  and  short-circuiting  the  break. 

With  the  primary  key  and  a  short-circuiting 
key  either  break  or  make  induced  currents  can 
be  used  as  stimuli  at  will. 

Unipolar  Induction 

1.  Arrange  the  inductorium  for  tetanizing 
currents  (posts  2  and  3).  Make  a  nerve-muscle 
preparation.  Lay  it  on  a  clean  dry  glass  plate. 
Let  the  nerve  rest  on  a  wire  connected  with  one 
pole  of  the  secondary  coil.  Set  the  inductorium 
in  action.  Connect  the  muscle  with  the  earth 
by  touching  the  muscle  with  the  end  of  a  wire, 
the  other  end  of  which  rests  on  a  gas  or  water 
pipe. 

The    muscle    will    show    tetanic    contractions, 


METHODS    OF    ELECTRICAL    STIMULATION         45 

provided  the  induced  current  is  sufficiently 
strong.  If  no  tetanus  is  seen,  move  the  second- 
ary coil  completely  over  the  primary. 

2.  Ligature  the  nerve  between  the  electrode 
and  the  muscle,  and  repeat  the  experiment. 

Stimulation  will  still  he  secured.  The  uni- 
polar discharge  passes  through  the  entire  length 
of  nerve  and  muscle  to  or  from  the  point  at 
which  the  connection  with  the  earth  is  made,  and 
thus  stimulates  the  entire  preparation. 

DuBois-Eeymond,  who  was  the  first  to  make 
the  preceding  experiments,  pointed  out  that 
whenever  the  secondary  circuit  was  open  (i.  e. 
when  the  bridge  between  the  ends  of  the  second- 
ary  wire  was  up)  the  making  and  breaking  of 
the  primary  circuit  caused  free  electricity  to 
gather  on  the  ends  of  the  secondary  wire.  When 
the  electro-static  induction  becomes  great  enough 
the  electromotive  force  overcomes  the  resistance 
in  whatever  connecting  path  may  be  offered,  and 
the  electricity  passes  from  the  coil  to  the  earth. 
If  a  part  of  the  path  is  formed  by  irritable 
tissues,  they  will  of  course  be  stimulated. 

3.  The  quantity  of  electricity  passing  through 
the  nerve  may  be  increased  by  approximating 
the  coils  or  by  increasing  the  electrical  capacity 
of  the  conductor,  as  follows  :  — 

Eemove  the   connecting  wire  of  the  prepara- 


46      THE    PHYSIOLOGY    OF   MUSCLE    AND    NEKVE 

tion.  Set  the  inductorium  in  action.  Touch 
the  muscle  with  the  moistened  finger. 

Contraction  follows. 

Here  the  electrical  capacity  of  the  preparation 
is  increased  by  connecting  the  preparation  with 
the  human  body,  a  conductor  of  large  surface 
(and  through  it  with  the  earth).  A  similar 
result  is  obtained  by  unipolar  stimulation  of 
nerves  and  muscles  while  still  in  the  body  of 
the  animal,  as  in  many  physiological  experi- 
ments. It  is  not  necessary  that  the  surface  of 
the  conductor  be  enormously  large.  The  follow- 
ing experiment  shows  that  even  very  small  sur- 
faces will  suffice. 

4.  On  a  carefully  dried,  clean  glass  plate  lay 
four  nerve-muscle  preparations.  Let  the  nerve 
of  the  first  rest  on  a  single  wire  the  other  end  of 
which  is  fastened  in  one  of  the  binding  posts  of 
the  secondary  coil.  Place  the  end  of  the  second 
nerve  on  the  tendon  of  the  muscle  of  the  first 
preparation,  the  third  on  the  second  tendon,  and 
the  fourth  nerve  on  the  tendon  of  the  third. 
Eemove  the  secondary  coil  some  distance  (a  few 
centimetres)  from  the  primary,  and  set  the  in- 
ductorium in  action.  Gradually  approximate 
the  coils. 

As  the  tension  at  the  ends  of  the  secondary 
wire  increases  by  the  approximation  of  the  coils, 


METHODS   OF  BLECTEICAL   STIMULATION       47 

the  first  preparation  will  contract.  On  further 
approximation,  the  first  and  second  ;  then  the 
first,  second,  and  third ;  and  finally  all  four  will 
contract. 

This  instructive  experiment  shows  that  when 
the  conducting  surface  is  small,  as  in  the  present 
instance,  the  unipolar  action  is  greater  on  the 
parts  nearer  the  secondary  wire  than  on  parts 
farther  away.  The  danger  of  unipolar  action  on 
tissues  lying  near  the  electrodes  in  ordinary 
artificial  stimulation  of  nerves  and  muscles  in 
situ  is  obvious. 

5.  It  is  not  even  necessary  that  the  conductor 
should  he  actually  in  contact  with  the  prep- 
aration. 

Connect  a  nerve-muscle  preparation,  insulated 
on  a  glass  plate,  with  one  pole  of  the  secondary 
coil,  and  set  the  inductorium  in  action.  The 
secondary  coil  should  completely  cover  the 
primary.  Bring  a  moistened  finger  as  near  the 
muscle  as  possible   without   touching  it. 

With  the  proper  intensity  of  the  primary  cur- 
rent, contraction  will  take  place,  though  absent 
when  the  finger  is  removed. 

The  sudden  approach  of  a  condenser  charged 
with  static  electricity  will  stimulate  an  isolated 
nerve  or  muscle. 

6.  The  danger  of  error  from  unipolar  action  is 


48   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

particularly  great  in  electrometer  observations  on 
the  current  of  rest  or  action  current  of  nerve  and 
muscle,  discussed  in  Chapter  VII.,  and  will  there 
be  demonstrated  experimentally. 

The  errors  due  to  unipolar  action  can  usually 
be  prevented  by  the  following  precautions  :  The 
secondary  coil  should  always  be  connected  with 
the  tissue  to  be  stimulated  through  a  short- 
circuiting  key,  which  should  be  kept  closed  ex- 
cept during  the  intentional  stimulation  of  the 
tissue.  With  this  good  metallic  connection  be- 
tween the  ends  of  the  secondary  wire  there  will 
be  no  static  electrification.  Further,  the  appear- 
ance of  positive  and  negative  electricity  during 
the  period  of  stimulation  must  be  provided 
against,  especially  if  that  period  is  at  all  pro- 
tracted, for  it  must  not  be  forgotten  that  the 
bridge  of  nerve,  which  completes  the  secondary 
circuit  by  uniting  the  two  electrodes,  possesses 
very  high  resistance,  and  thus  affords  but  an 
imperfect  closure  of  the  ends  of  the  secondary 
wire.  This  provision  is  made  by  connecting  the 
positive  electrode  with  the  earth  by  a  good  con- 
ductor, for  example,  by  a  copper  wire  leading 
from  the  electrode  to  the  gas  or  water  pipe. 
In  case  ©f  doubt,  a  control  experiment  should 
be  made.  The  nerve  should  be  severed  between 
the   stimulated  point  and  the  muscle,  and  one 


METHODS   OF   ELECTRICAL   STIMULATION  49 

end  laid  on  the  other.  Excitation  through  the 
passage  of  a  nerve  impulse  along  the  nerve  is 
thereby  made  impossible.  If  the  muscle  still 
contracts  when  the  nerve  is  stimulated  above 
the  section,  it  is  because  of  unipolar  stimulation. 

An  additional  reason  for  care  is  that  the  insu- 
lation of  the  secondary  spiral  is  injured  by  leav- 
ing the  secondary  circuit  open  while  the  hammer 
of  the  inductorium  is  in  action. 

It  may  be  stated  that  the  direction  of  the  uni- 
polar discharge  is  of  importance.  Excitation 
takes  place  only  where  the  positive  charge  enters 
the  nerve  or  the  negative  charge  leaves  the  nerve. 

The  break  induction  current  is  more  effective 
than  the  make,  as  the  slower  development  of  the 
latter  causes  the  terminals  of  the  secondary  wire 
to  be  charged  more  slowly  than  by  the  rapidly 
developed  break  current. 

Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate. 
Zinc  wire,  4  inches  long.  Copper  wire,  4  inches  long. 
Porcelain  dish.  Mercury  v  bot  sulphuric  acid.  5%  solu- 
tion of  potassium  chromate.  Iron  wire,  4  inches  long. 
Muscle  clamp.  lion  stand.  Capillary  electrometer.  Rheo- 
cord.  Microscope  (micrometer  ocular,  objective  3)  Dan- 
iell  cell.  Dry  cell.  Two  platinum  electrodes.  Zinc  elec- 
trode. Beaker.  Sodium  chloride.  Simple  key.  9  wires, 
2  feet  long.  Saturated  solution  of  copper  sulphate. 
4 


50   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

Pole-changer  (in  paper  dish).  Filter  paper  saturated  with 
starch  paste  containing  potassium  iodide.  Inductorium 
(with  electrodes).  Coil  with  few  windings  (primary  coil 
of  a  second  inductorium).  Bar  magnet.  Iron  filings. 
Galvanometer.  Card,  with  thick  copper  wire.  Ligatures. 
Frogs. 


THE    GRAPHIC    METHOD 


51 


III 


THE   GRAPHIC    METHOD 


:^^^3» 


O- 


The  studies  next  to  be  undertaken  make  use  of 
the  change  of  form  of  the  con- 
tracting muscle  as  a  partial 
index  to  the  transformation 
of  energy  in  the  tissue.  A 
permanent  record  is  desirable. 
Further,  the  changes  in  the 
dimensions  of  the  muscle  are 
so  small  that  it  is  necessary 
to  have  the  graphic  record  en- 
larged, rather  than  of  actual 
size.  To  satisfy  these  condi- 
tions, the  muscle  is  attached 
near  the  fulcrum  of  a  lever 
furnished  with  a  recording 
point.  The  surface  for  the 
writing  is  usually  glazed  pa- 
per which   has   been   covered 

*    t  the  friction  bearing.     It 

With    a    thin    layer    of    SOOt    by      can  then  be  revolved  rap- 

,        .  idly  by  hand  (spun)  at 

passing  the  paper  through  the    a    sufficiently   uniform 

luminous  part  of  a  broad  gas    Sl'ee(1, 

flame.     The  paper  is  fastened  (before  smoking) 


Fig.  11.  The  kymo- 
graph or  record  dram. 
The  aluminium  drum  is 
driven  by  clbckwork  at 
speeds  varying  from  one 
revolution  per  hour  to 
eight  per  minute.  The 
brass  tube  or  sleeve  on 
which  it  is  held  by  a 
spring  clip  rests  below 
on  a  disk  fastened  to 
a  steel  spindle  which 
passes  through  the  whole 
length  of  the  sleeve.  By 
turning  the  screw  at  the 
top  the  sleeve  with  the 
drum   can  be  raised  off 


52   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

on  a  plate  or  on  a  drum  which  moves  past  the 
writing  point  ancL  furnishes  thus  a  continuously 
fresh  surface.1 

1  The  paper  is  cut  wider  and  longer  than  the  surface  of  the 
drum.  The  extra  width  is  to  protect  the  bearings  of  the  drum 
from  soot  that  might  otherwise  collect  there  in  smoking  the 
paper.  The  extra  length  allows  the  edge  of  the  overlap  to  be 
gummed  to  the  paper  below,  permits  the  paper  to  be  removed 
from  the.  drum  by  cutting  through  the  overlap  parallel  to  the 
mucilage,  — the  surface  of  the  drum  being  protected  from  the 
knife  by  the  underlying  paper,  — and  provides  an  unsmoked 
surface  by  which  the  paper  can  be  handled  on  its  removal  from 
the.  drum.  The  drum  should  be  laid  in  the  centre  of  the  strip 
of  paper,  the  gummed  edge  to  the  left,  and  the  axis  of  the  drum 
precisely  at  right  angles  to  the  long  axis  of  the  paper ;  the 
mucilage  should  be  moistened,  and  the  ends  of  the  paper 
brought  around  and  fastened.  If  the  paper  is  awry,  the  sur- 
face will  not  lie  uniformly  against  the  drum  and  the  record 
will  be  deformed.  The  drum  should  now  be  placed  in  the 
smoking  apparatus,  revolved  uniformly  and  not  too  fast, 
brought  over  the  gas  flame,  lowered  just  below  the  upper  edge 
of  the  flame,  and  covered  with  a  chocolate  brown  layer  of  soot, 
beginning  at  the  operator's  left  hand  and  passing  gradually  to 
the  right.  The  speed  should  be  such  that  one  passage  from 
left  to  right  shall  suffice.  To  trim  the  edges,  hold  the  drum 
in  the  left  hand,  inclined  downwards,  and  pass  a  sharp  knife- 
blade  around  the  lower  edge.  The  handle  of  the  knife  should 
be  kept  lower  than  the  blade,  to  avoid  tearing.  In  removing 
the  paper  from  the  drum,  hold  the  drum  in  the  air  with  the 
left  thumb  pressed  on  the  edge  of  the  paper  near  the  overlap, 
and  cut  through  the  overlapping  edge  near  the  mucilage.  The 
loosened  paper  will  hang  down  and  may  then  be  seized  by  the 
unsmoked  overlap.  In  recording,  let  all  the  curves  begin  near 
the  overlap.  Attentiou  to  these  details  is  indispensable  to  the 
best  technical  results. 


THE    GRAPHIC    METHOD  53 

Xhe  writing  point  rubs  off  the  soot  in  its  path 
and  leaves  a  white  magnified  tracing  of  the 
muscle's  change!  in  length  or  whatever  dimen- 
sion is  the  subject  of  record.  The  paper  is  then 
removed,  drawn  through  a  saturated  solution  of 
white  shellac  in  95  per  cent  alcohol,1  and  hung 
up  until  the  alcohol  is  evaporated.  The  soot 
will  be  covered  over  thereby,  and  held  in  place 
by  a  thin  layer  of  shellac,  and  the  record  will 
be  secure. 

The  graphic  record  involves  the  use  of  appa- 
ratus. It  never  should  be  forgotten  that  the  use 
of  apparatus  always  introduces  more  or  less 
error.  In  every  experiment  the  apparatus 
should  be  criticised  sharply.  The  numerous 
imperfections  which  such  scrutiny  will  bring 
to  light  are  of  two  sorts,  —  the  errors  that  may 
be  neglected,  and  the  errors  that  may  not  be 
neglected  without  seriously  impairing  the  value 
of  the  method  for  the  purpose  in  hand.  For 
example,  a  count  of  the  pulse  rate  with  an  ordi- 
nary watch  will  usually  be  incorrect  by  one  or 
two  beats  in  the  minute,  but  such  a  record  is 
quite  accurate  enough  for  most  purposes.  The 
use  of  a  stop-watch  marking  fifths  of  seconds 
would  add  nothing  to  the  value   of  the  count, 

1  To  make  this  solution,  the  alcohol  should  he  allowed  to 
stand  on  the  shellac  a  month  or  more  hefore  using. 


54      THE    PHYSIOLOGY    OF   MUSCLE   AND    NERVE 

for  the  error  introduced  by  numberless  causes 
that  slightly  modify  the  heart  beat  from  minute 
to  minute  is  greater  than  the  error  introduced 
by  using  an  ordinary  watch  instead  of  a  stop- 
watch. The  correction  of  errors  that  are  too 
small  to  alter  essentially  the  value  of  the 
method  for  the  purpose  to  which  it  is  applied 
is  usually  wasteful. 

With  these  points  in  mind,  smoke  a  drum. 
Arrange  the  inductorium  with  simple  key  for 
maximal  break  induction  currents.  Prepare  a 
gastrocnemius  muscle,  fasten  it  in  the  muscle 
clamp,  tie  a  fine  copper  wire  around  the  ten  do 
Achillis,  wrap  the  wire  about  the  hook  on  the 
muscle  lever,  and  fasten  the  end  in  the  binding 
post  on  the  handle  of  the  lever  (Fig.  13,  page 
60).  Connect  the  secondary  coil  with  the  posts 
on  the  muscle  clamp  and  muscle  lever  respec- 
tively. Weight  the  muscle  with  ten  grams.  Ar- 
range the  lever  to  write  on  the  drum.  Eecord 
single  contractions  with  various  speeds. 

Note  that  the  muscle  writes  its  contraction  in 
the  form  of  a  curve,  the  ordinates  of  which  mea- 
sure the  height  to  which  the  load  is  lifted. 

Start  the  drum  at  very  rapid  speed.  Bring 
the  writing  point  of  the  vibrating  tuning  fork 
(Fig.  12)  against  the  paper  below  the  point  of  the 
muscle  lever,  and  stimulate  the  muscle  to  contract. 


THE    GRAPHIC   METHOD  55 

Observe  that  the  tuning  fork  now  gives  the 
time  intervals  on  the  abscissa  of  the  muscle 
curve,  from  which  the  duration  of  the  periods 
of  shortening  and  relaxation  may  be  known. 
Note  also  the  difference  in  appearance  of  the 
curves  taken  on  a  slow  and  a  rapidly  moving 
surface. 

Measure  the  interval  between  the  begin- 
ning of  contraction  and  the  point  of  maximum 
shortening. 

Write  a  critical  account  of  the  muscle  lever 
in     your    laboratory 
note-book. 

Compare    this   ac-  ■*"■  The  tll»iu«-folk- 

count  with  the  remarks  which  follow  :  — 

The  object  of  the  muscle  lever  is  to  write  a 
magnified  record  of  the  change  in  form  of  the 
muscle.  Usually  the  muscle  is  suspended  in  a 
muscle  clamp  and  its  lower  end  attached  to 
the  lever,  which  then  records  the  shortening  of 
the  muscle.  The  same  lever  may  be  used  to 
record  the  thickening  of  the  muscle ;  in  this 
case  the  muscle  is  of  course  horizontal  and 
the  lever  rests  upon  it.  For  either  purpose 
the  weight  of  the  lever  is  an  objection,  for 
it  tends  to  prevent  the  muscle  from  begin- 
ning its  movement  (inertia  of  position).  Once 
in  motion,  the  weight  tends  to  keep  moving, 
and  thus  to  continue  the  record  of  contraction 


56   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEKVE 

after  the  actual  contraction  has  ceased  (inertia 
of  motion).  As  the  inertia  of  motion  increases 
with  the  mass  and  the  square  of  the  velocity, 
the  lighter  the  lever  the  less  the  error.  The 
disposition  of  the  weight  relative  to  the  axis 
is  also  of  importance.  In  a  swinging  system, 
the  nearer  the  mass  to  the  axis  of  rotation,  the 
less  are  the  after  vibrations  or  pendulum-like 
oscillations  which  continue  after  the  original  im- 
pulse has  ceased.  For  this  reason,  in  experi- 
ments likely  to  be  disturbed  by  after  vibrations, 
the  weight  which  the  muscle  lifts  is  attached  to 
the  small  pulley,  so  as  to  be  as  near  the  axis  as 
possible.  In  this  case,  the  weight  on  the  muscle 
is  of  course  not  the  weight  hung  on  the  pulley ; 
the  pulley  weight  must  be  divided  by  the  num- 
ber of  times  the  radius  of  the  pulley  is  contained 
in  the  distance  between  the  axis  aiid  the  point  of 
attachment  of  the  muscle  to  the  lever. 

It  will  be  observed  that  the  writing  point  is  a 
strip  of  tinsel  bent  slightly  and  placed  parallel 
to  the  writing  surface.  It  is  very  easily  moved 
in  a  direction  at  right  angles  to  the  writing  sur- 
face, but  resists  movement  in  a  vertical  direction. 
The  bend  makes  the  strip  a  weak  spring,  ena- 
bling the  point  to  remain  in  contact  with  the 
drum  throughout  the  excursion  of  the  point  on 
the  paper.  The  writing  point  should  be  as  nearly 
as  possible  parallel  to  the  paper.     Even  in  this 


THE   GRAPHIC    METHOD  57 

position,  the  distance  of  the  end  of  the  straw 
from  the  paper  is  necessarily  Less  when  the  lever 
is  horizontal  than  when  rais.-d  by  the  contrac- 
tion of  the  muscle,  for  the  end  of  the  lever 
describes  a  curved  line  in  a  plane  tangent  to  the 
recording  surface.  Were  it  not  for  the  spring 
of  the  writing  point,  the  latter  would  leave  the 
drum.  To  remain  on  the  drum  at  the  height  of 
the  contraction,  the  point  must  at  the  beginning 
of  contraction  press  against  the  drum  with  much 
more  friction  than  is  necessary  simply  for  scratch- 
ing through  the  layer  of  soot.  Thus  the  distance 
of  the  writing  point  from  the  axis  is  constantly 
varying,  and  the  magnification  of  the  lever 
is  constantly  changing.  Within  the  limits  ordi- 
narily employed  in  physiology,  the  deformation 
of  the  curve  thereby  produced  is  proportional  to 
the  length  of  the  arc  through  which  the  point 
moves ;  the  curve  should  therefore  be  written 
no  larger  than  is  necessary  for  clearness. 

When  the  smoked  surface  is  at  rest,  and  the 
contracting  muscle  lifts  the  lever,  the  writing 
point  describes  an  arc  ;  when  the  muscle  relaxes, 
the  writing  point  returns  in  the  same  line.  When 
the  drum  revolves,  the  writing  point  describes  a 
curve  as  the  muscle  contracts.  The  maximum 
shortening  of  the  muscle,  or  height  to  which  the 
load  is  lifted,  is  measured  by  a  perpendicular 
drawn  Erom  the  highest  point  of  the  curve  t<>  the 


58      THE   PHYSIOLOGY    OF   MUSCLE   AND    NERVE 

abscissa.  The  time  required  for  the  muscle  to 
reach  this  height,  however,  is  not  the  distance  on 
the  abscissa  from  the  beginning  of  the  curve  to 
the  perpendicular,  but  to  the  point  at  which  the 
segment  of  a  circle  of  a  radius  equal  to  the 
length  of  the  lever  would  cut  the  abscissa  when 
drawn  from  the  highest  point  of  the  curve.  Prac- 
tically, this  measurement  is  made  by  turning  the 
drum  back  until  the  point  of  the  raised  lever 
rests  at  the  summit  of  the  curve,  and  then,  while 
the  drum  is  at  rest,  allowing  the  lever  to  write 
the  ordinate  by  falling  down  to  the  abscissa. 

Perpendicular  ordinates  may  be  secured  by  a 
long  pin  passed  transversely  through  the  end  of 
the  writing  lever,  and  bent  twice  at  right  angles, 
first  parallel  to  the  paper  and  then  towards  it. 
The  lever  is  perpendicular  to  the  paper  and  very 
near  it ;  the  weight  of  the  pin  keeps  the  point 
against  the  paper  as  the  lever  rises.  The  perpen- 
dicular writing  has  many  faults  in  common  with 
arc  writing. 

Apparatus 

Normal  saline.  Bowl.  Pipette.  Towel.  Glass  plate. 
Kymograph.  Glazed  paper.  Smoking  apparatus.  Shel- 
lacking trough.  Shellac  in  alcohol.  Muscle  lever  (weight 
pan).  Muscle  clamp.  Stand.  Inductorium.  Electrodes. 
Simple  key.  Dry  cell.  5  wires.  Fine  copper  wire.  Ten 
gram  weight.     Tuning  fork.     Tin  foil.     Cement.     Frogs. 


STIMULATION    OF   MUSCLE   AND    NEKVE.  59 


IV 


THE  ELECTRICAL  STIMULATION  OF   MUSCLE 
AND  NERVE 

The  Galvanic  Current 

The  study  of  the  changes  occasioned  in  muscle 
and  nerve  by  electrical  stimulation  may  profit- 
ably begin  with  the  action  of  the  galvanic 
current. 

Non-Polarizable  Electrodes.  ■ —  When  metal 
electrodes  come  in  contact  with  an  electro- 
lyte, polarization  currents  develop  (see  page  25). 
Electrodes  of  metal  for  this  reason  should  be 
avoided  in  the  study  of  the  effect  of  the  galvanic 
current  on  muscle  and  nerve.  A  "non-polar- 
izable  "  electrode  should  be  employed.  Strictly 
speaking,  no  electrode  is  non-polarizable,  but 
practically  the  polarization  errors  are  excluded 
by  the  following  device :  A  small  brush  of 
camel's  hair  from  which  the  quill  and  other 
wrappings  have  been  removed  is  passed,  point 
first,  through  the  large  end  of  a  glass  tube, 
about  two  inches  long,  the  other  end  of  which 


60      THE    PHYSIOLOGY   OF   MUSCLE    AND    NERVE 

has  been  drawn  out  to  a  diameter  about  that  of 
the    thick    end   of   the   brush.       The    latter    is 


Fig.  13.  The  moist  chamber  with  non-polarizable  brush  electrodes  and 
muscle  lever.  The  glass  cover  of  the  chamber  has  been  omitted  for  the 
sake  of  clearness. 


STIMULATION    OF    MUSCLE    AND    NERVE  61 

brought  through  the  drawn-out  end  of  the  tube 

until  it  is  held  fast  by  the  glass.  The  tube  for  a 
short  distance  above  the  brush  is  packed  with 
potter's  clay  moistened  with  (•.(">  per  cent  solu- 
tion of  sodium  chloride.  The  tube  is  now  partly 
filled  with  saturated  solution  of  zinc  sulphate 
and  an  amalgamated  zinc  wire  provided  with  a 
binding  post  is  inserted  and  held  in  place  by  a 
piece  of  rubber  tubing,  as  drawn  in  Fig.  13. 
Finally,  the  brush  is  wet  with  the  saline 
solution. 

Opening  and  Closing  Contraction.  —  Smoke  a 
drum.  Arrange  the  muscle  lever  to  write  on 
the  smoked  paper.  Make  two  non-polarizable 
electrodes  (the  hands  which  touch  the  clay 
should  be  scrupulously  clean  ;  metal  instru- 
ments should  not  be  used).  Fasten  the  elec- 
trodes by  means  of  the  spring  clips  to  the 
glass  plate  of  the  nerve-holder.  Connect  them 
through  an  open  simple  key  with  the  pole-  of 
a  dry  cell.  Prepare  a  sartorius  muscle  (Fig.  14) 
the  nerve-endings  in  which  have  been  paralyzed 
with  curare,  preserving  the  pelvic  and  tibial  at- 
tachments. Fasten  the  piece  of  pelvic  bone  in 
the  muscle  clamp.  Let  the  ends  of  the  elec- 
trodes rest  on  the  muscle.  To  the  tibial  end  tie 
a  thread,  and  fasten  the  thread  to  the  upright 
pin  of  the  muscle  lever,  so  that  the  horizontal 


62      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 


muscle  may  write  its  curve  on  the  drum.     Close 

the  key.  Turn  the 
drum  by  hand  about 
5  mm.     Open  the  key. 

The  muscle  will 
twitch  when  the  cur- 
rent is  made  and  prob- 
ably when  it  is  broken, 
but  during  the  passage 
of  the  current  there 
will  be  no  contraction. 

This  would  seem  to 
indicate  that  the  mus- 
cle is  stimulated  only 
by  a  sudden  change  in 
the    intensity    of    the 

Fig.  14.  Hind  limb  of  frog,  anterior    current     (DuBois-Eey- 
view  (Ecker-Wiedersheim).  . 

mono).     Into  this  im- 
portant matter,  we  must  inquire  at  some  length. 

Changes  in  Intensity  of  Stimulus.  —  1.  Sudden 
change,. ,  Connect  the  zinc  of  a  dry  cell  through 
an  open  simple  key  (Fig.  15,  a), 
with  one  of  the  electrodes  of  the 
preceding  experiment  and  the  car- 
bon with  one  post  of  a  closed  short- 
circuiting  key  (Fig.  15,  b).  Connect 
this  same  post  with  the  zinc  of  another  cell. 
Connect  the  remaining  post  with  the  carbon  of 
the  second  cell  and  with  the  remaining  electrode. 


Fig.  15. 


STIMULATION   OF    MUSCLE   AND   NEKVE         63 

Close  A. 

The  muscle  will  contract 

Open  B3  thus  suddenly  increasing  the  strength 
of  the  current. 

The  muscle  will  again  contract. 

2.  Gradual  change.  Lead  from  the  outer  zinc 
and  carbon  of  two  cells  coupled  in  series  (zinc 
to  carbon)  to  the  0  and  1  metre  posts  of  the 
rheocord,  through  an  open  simple  key  (Fig. 
16).  Note  that  only  one-tenth  the  wire  in  the 
rheocord  is  included  in  the  circuit ;  the  resis- 
tance of  the  entire  length  (10 
metres)  would  be  too  great. 
Bring  the  slider  close  to  the 
post  0,  so  that  only  a  small 
fraction  of  the  current  can 
flow  through  the  electrodes. 
Place  the  electrodes  on  the 
muscle.  Close  the  key.  The  muscle  contracts. 
Move  the  slider  very  gradually  along  the  wire 
until  all  the  current  possible  passes  through 
the  muscle. 

There  will  be  no  contraction. 

With  Indirect  Stimulation.  —  1.  Smoke  a  drum. 
Make  a  nerve-muscle  preparation  (sciatic  nerve 
and  gastrocnemius  muscle).  Place  the  femur  in 
the  clamp  in  the  moist  chamber.  Let  the  nerve 
rest  on  non-polarizable  electrodes  connected 
through  an  open   key   with   a   dry   cell.     Attach 


64   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEEVE 

the  tendo  Achillis  to  the  muscle  lever.  .  Let  the 
muscle  lever  write  on  a  slowly  moving  drum. 
Close  and  open  the  key. 

Both  closing  and  opening  contraction  will  be 
seen.  (If  the  frog  has  been  brought  from  a  cold 
room  into  the  warm  laboratory,  opening  and 
closing  tetanus  will  probably  replace  the  usual 
twitch.     See  page  108.) 

2.  Eepeat  Experiment  2,  page  63,  using  the 
nerve-muscle  preparation  instead  of  the  curarized 
muscle. 

It  will  again  be  found  that  the  intensity  of 
the  current  must  be  increased  with  a  certain 
rapidity  in  order  to  stimulate. 

The  experiments  just  made  support  DuBois- 
Keymond's  statement  that  the  electrical  current 
does  not  stimulate  during  the  entire  period  of 
its  flow  through  the  irritable  tissue,  but  only 
when  the  intensity  is  rapidly  altered  by  making 
or  breaking  the  circuit.  These  experiments, 
however,  were  made  on  the  rapidly  reacting 
skeletal  muscle  of  the  frog.  The  law  does  not 
hold  good  for  sluggish  contractile  tissue.  In- 
deed it  can  be  disproved  even  for  highly  striated 
muscle  by  a  very  careful  examination  of  the 
manner  in  which  excitation  takes  place.  Prliiger 
discovered  that  when  the  galvanic  current  is 
made,  excitation  takes  place  only  at  the  points 


STIMULATION   OF   MUSCLE   AND   NERVE 


65 


through  which  the  current  leaves  the  muscle  or 
nerve  (cathodal  stimulation),  and  that  when  the 
current  is  broken,  excitation  takes  place  only 
where  the  current  enters  the  irritable  tissue. 
This  "  polar  excitation  "  we  must  now  consider. 
We  shall  find,  among  many  other  facts,  the 
refutation  of  the  idea  that  stimulation  does  not 
occur  throughout  the  passage  of  the  current. 


Fig.  17.    The  cork  clamp,  with  muscle  attached  to  muscle  lever. 


Polar  Stimulation  of  Muscle 

1.  Slit  the  curarized  sartorius  muscle  trouser- 
like  from  the  lower  end.  Lay  it  on  a  glass  plate. 
Bring  one  non-polarizable  electrode  against  each 
leg.     Make  and  break  the  current. 


66      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

On  making  the  current  the  cathodal  side  will 
contract ;  on  breaking,  the  anodal  side. 

2.  Lay  the  muscle  on  ice  covered  with  a  small 
piece  of  paraffin  paper,  to  shield  the  muscle  from 
water.  When  thoroughly  cold,  place  the  muscle 
in  the  cork  clamp  (Fig.  17),  making  very  gentle 
pressure  across  the  middle,  and  bring  the  non- 
polarizable  electrodes  against  the  ends.  Make 
and,  after  a  minute,  break  the  current. 

The  excitation  wave  passes  so  slowly  through 
cooled  muscle  that  the  contraction  can  be  seen 
with  the  unaided  eye  to  begin  at  the  cathode  on 
closing  and  at  the  anode  on  opening  the  circuit. 

3.  Ureter.1  —  Place  the  extirpated  ureter  of 
any  mammal  on  a  glass  plate  set  as  a  cover  on 
a  beaker  containing  hot  normal  saline  solution, 
so  that  the  hot  vapor  of  the  water  shall  keep 
the  ureter  warm.  Bring  the  non-polarizable 
electrodes  against  the  ureter.  Note  which  elec- 
trode is  the  cathode.     Close  the  key. 

After  a  distinct  latent  period  the  ureter  in  the 
cathodal  region,  and  nowhere  else,  will  contract, 
and  the  contraction  wave  will  spread  from  the 
cathode  in  both  directions  along  the  ureter. 

Open  the  key. 

1  The  experiment  succeeds  also  with  extirpated  pieces  of  in- 
testine about  four  inches  long,  provided  they  are  kept  warm 
with   normal   saline  solution. 


STIMULATION    OF   MUSCLE    AND    NEKVE  67 

The  contraction  takes  place  now  only  at  the 
anode,  and  the  contraction  wave  spreads  from 
that  point  over  the  muscle  (as  making  the  cur- 
rent is  a  less  effective  stimulus  than  breaking, 
it  may  be  necessary  to  increase  the  strength  of 
the  current,  or  to  keep  it  closed  a  considerable 
time,  in  order  to  secure  making  contraction). 

4.  Intestine.  —  Place  the  non-polarizable  anode 
on  the  intestine  of  a  freshly  killed  rabbit,  the 
cathode  on  some  indifferent  point,  for  example, 
the  liver.     Close  the  key. 

The  intestine  will  constrict  in  the  anodal  re- 
gion and  remain  constricted  during  the  passage 
of  the  current,  provided  it  be  not  so  long  as  to 
cause  fatigue.  A  peristaltic  contraction  wave 
usually  passes  from  the  anode  in  both  directions 
along  the  intestine. 

Place  the  cathode  on  the  intestine,  and  the 
anode  on  an   indifferent  point.      Close  the  key. 

A  small,  indistinct  thickening  will  be  seen  in 
the  cathodal  region. 

Thus  the  intestine,  while  it  serves  admirably 
to  illustrate  a  polar  action  of  the  galvanic  cur- 
rent, apparently  differs  from  the  tissues  already 
considered  in  that  closure  causes  contraction  at 
the  anode  instead  of  the  cathode.  The  exception 
is  only  apparent,  and  its  explanation  is  that  the 
point  at  which  the  electrode  touches  the  peri- 


68   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 


toneal  surface  of  the  many-layered  intestinal 
wall  is  not  the  physiological  anode  or  cathode ; 
i.  e.  not  the  point  at  which  the  current  actually 
enters  or  leaves  the  muscular  coat.  This  matter 
is  discussed  on  page  71. 

5.  Smoke  a  drum.  Eaise  the  drum  off  the 
friction  bearing  by  turning  the  screw  at  the  top 
of  the  shaft  to  the  right.     Arrange  two  muscle 

levers  and  the 
electromagnetic 
signal  (Fig.  18)  to 
write  on  the  drum 
in  the  same  verti- 
cal line.  Place 
the  signal  in  the 
circuit  between 
one  dry  cell  and 
the  rheocord; 
otherwise  let  the 
electrical  connections  be  as  in  Fig.  16,  page  63. 
Bring  the  slider  near  the  positive  post  of  the 
rheocord.  Fasten  a  curarized  sartorius  muscle  by 
the  middle  in  the  cork  clamp ;  the  pressure  should 
be  enough  to  prevent  the  contraction  wave  of 
one  part  reaching  the  other  part,  but  not  great 
enough  to  prevent  the  passage  of  the  excita- 
tion. Secure  the  cork  clamp  in  the  jaws  of  the 
muscle   clamp  in  such  a  way  that  the  muscle 


Fig.  18.    The  electromagnetic  signal. 


STIMULATION    OF   MUSCLE    AND    NERVE  69 

shall  be  vertical  to  the  writing  levers.  Tie  a 
thread  around  the  pelvic  and  tibial  fragments 
and  fasten  each  thread  to  a  muscle  lever,  so  that 
each  half  of  the  muscle  may  record  its  contrac- 
tion independently  of  the  other.  Let  the  brush 
of  one  of  the  non-polarizable  electrodes  rest  on 
each  end  of  the  muscle.  Note  which  lever  is 
connected  with  the  cathodal  end.  Make  the 
current.  If  the  muscle  does  not  contract,  move 
the  slider  along  the  wire  a  short  distance  towards 
the  positive  post  (so  as  to  bring  a  stronger 
current  through  the  electrodes)  and  make  the 
current  again.  When  both  make  and  break 
contractions  are  secured,  see  that  the  writing 
points  record  properly,  and  "  spin "  the  drum, 
but  not  too  fast.  As  soon  as  the  drum  moves 
steadily,  make  and  then  break  the  current. 

The  moment  of  making  and  breaking  the  cur- 
rent will  be  recorded  by  the  electromagnetic 
signal.  An  instant  later  the  muscle  levers  will 
begin  their  record  of  the  contractions. 

It  will  be  found  that  the  cathodal  half  of 
the  muscle  contracts  first  on  closing,  the  anodal 
half  mi  opening  the  current.  Evidently  the 
excitation  began  on  closure  at  the  cathode  and 
passed  thence  to  the  anode,  while  on  opening 
the  circuit  the  excitation  began  at  the  anode 
and  passed  to  the  cathode. 


70   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEKVE 

In  order  to  measure  this  interval  accurately 
the  drum  should  be  turned  back  until  the  writ- 
ing point  of  the  signal  lies  precisely  in  the  ordi- 
nate drawn  by  it  during  the  experiment.  The 
muscle  should  then  be  stimulated.  The  ordinate 
now  drawn  by  the  muscle  with  the  drum  thus 
at  rest  will  be  synchronous  with  that  drawn  by 
the  signal  during  the  experiment,  and  will  mark 
upon  the  abscissa  of  the  muscle  curve  the  moment 
of  stimulation. 

6.  Tonic  Contraction.  —  Connect  a  dry  cell 
through  an  open  simple  key  with  the  metre 
posts  of  the  rheocord.  Connect  non-polarizable 
electrodes  with  the  positive  post  and  the  slider. 
Fasten  one  end  of  the  curarized  sartorius  (pre- 
pared with  fragments  of  pelvis  and  tibia  attached) 
in  the  muscle  clamp.  Tie  a  thread  to  the  other 
end  and  fasten  the  thread  to  the  upright  pin  of 
the  muscle  lever.  Let  non-polarizable  electrodes 
rest  on  the  muscle  near  the  respective  ends. 
Use  a  strength  of  current  that  will  just  cause 
contraction  on  closure.  Watch  very  closely  the 
cathodal  region  near  the  junction  of  the  muscle 
fibres  with  the  tendon.     Close  the  key. 

After  the  closing  contraction,  the  ends  of  the 
muscle  fibres  next  the  tendon  in  the  cathodal 
region  will  show  a  faint  but  distinct  thickening, 
which  will  remain  until  the  current  is  broken. 


STIMULATION   OF   MUSCLE   AND   NERVE  71 

These  several  experiments  demonstrate  that  in 
galvanic  stimulation  of  both  skeletal  and  smooth 
muscle  the  excitation  takes  place  at  the  points 
where  the  current  leaves  and  enters  the  muscle. 
Before  inquiring  whether  this  law  holds  good  for 
the  heart,  the  muscle  culls  in  which  have  a  form 
intermediate  between  the  smooth  muscle  cell  and 
the  cells  of  skeletal  muscle,  it  will  be  necessary 
to  consider  whether  the  points  of  contact  with  the 
electrodes* are  always  the  real  anode  and  cathode. 

Physiological  Anode  and  Cathode.  —  When  the 
electrodes  are  placed  directly  on  a  nerve,  or  are 
applied  to  a  muscle  witli  straight  parallel  fibres  in 
such  a  way  that  the  current  flows  through  each 
fibre  from  end  to  end,  the  anode  and  cathode 
obviously  coincide  with  the  points  at  which  the 
electrodes  touch  the  muscle.  When,  however, 
the  fibres  are  of  irregular  shape,  or  are  irregularly 
disposed,  the  current  lines  can  no  longer  traverse 
the  fibres  from  end  to  end,  but  will  enter  and 
leave  fibres  at  points  other  than  those  in  contact 
with  the  electrodes. 

The  difference  between  the  operator's  elec- 
trodes and  the  physiological  anode  and  cathode 
is  also  obvious  when  the  electrodes  are  applied 
to  skin,  connective  tissue,  mucous  membrane,  etc., 
covering  the  muscle  or  nerve,  —  the  points  at 
which   the   electrodes  touch  the  covering  tissue 


72   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

cannot  be  the  points  at  which  the  current  actu- 
ally leaves  or  enters  the  muscle. 

The  failure  to  keep  this  distinction  in  mind 
may  lead  to  wholly  erroneous  interpretations. 
Thus  when  the  ureter  is  extirpated,  or  is  raised 
from  the  tissues  on  which  it  normally  rests,  its 
reaction  to  the  galvanic  current  follows  the  law, 
—  contraction  begins  at  cathode  on  making,  at 
anode  on  breaking  the  current;  but  when  the 
ureter  is  stimulated  in  situ,  exactly  the  opposite 
effect  is  seen,  —  contraction  begins  at  anode  on 
making  the  current.  The  explanation  is  that  the 
current  lines  in  the  latter  case  are  very  widely 
diffused  through  the  conducting  tissues  on  which 
the  ureter  lies,  so  that  the  current  passes  into 
and  out  of  the  muscle  fibres  for  some  distance 
either  side  of  the  positive  electrode.  Each  point 
at  which  the  current  leaves  a  fibre  is  a  secondary 
cathode,  and  if  the  number  of  such  points  is 
large,  cathodal  stimulation  will  take  place  in 
what,  superficially  regarded,  is  the  anodal  region 
(compare  page  93,  and  Fig.  27).  The  same  ex- 
planation holds  good  for  the  intestine  (see  page 
67).  The  formation  of  physiological  anodes  and 
cathodes  is  well  shown  in  the  next  experiment. 

Physiological  Anodes  and'  Cathodes  in  Rectus 
Muscle. — Eemove  the  rectus  abdominis  muscle. 
Note  the  tendinous  bands  that  cross  the  muscle 


STIMULATION   OF   MUSCLE   AND   NEKVE  73 

from  side  to  side  and  divide  it  into  parts.  Lay 
the  muscle  smoothly  on  a  glass  slide.  Connect 
the  non-polarizable  electrodes  through  a  simple 
key  with  a  dry  cell.  Place  one  electrode  on  each 
end  of  the  muscle.     Close  the  key. 

On  closure,  the  cathodal  side  of  each  division 
of  the  muscle  will  show  a  sharply  defined  con- 
tinued contraction  of  the  ends  of  the  fibres  at 
their  insertion  in  the  transverse  tendinous  bands. 
On  opening,  the  cathodal  contraction  disappears, 
and  a  similar  thickening  of  the  fibres  is  seen  at 
the  anodal  side  of  each  division.  The  twitch  of 
each  segment  on  closure  and  opening  of  the  cur- 
rent also  starts  respectively  from  the  cathodal 
and  anodal  ends  of  each  segment.  These  effects 
are  best  seen  through  a  magnifying  glass. 

Polar  Stimulation  in  Heart.  —  The  muscle  cells 
of  the  heart  are  not  only  of  irregular  shape,  but 
they  are  so  joined  with  each  other  as  to  make  it 
impossible  to  pass  a  current  through  the  heart 
muscle  without  the  current  lines  cutting  fibres 
in  every  direction.  It  would  seem  therefore  that 
secondary  anodes  and  cathodes  would  be  formed 
to  such  a  degree  that  the  demonstration  of  polar 
excitation  would  be  difficult  or  impossible. 
Experimentation  shows  however  that  this  is  not 
the  case.  The  heart  behaves  like  a  single  hollow 
fibre. 


74   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEKVE 

Monopolar  Method.  —  The  small  size  and  conical 
form  of  the  ventricle  of  the  frog's  heart  make  the 
ordinary  method  of  stimulation,  in  which  the  elec- 
trodes would  both  be  placed  on  the  heart,  less  suit- 
able than  the  monopolar  method.  This  method 
was  suggested  by  the  fact  that  the  stimulating 
effect  of  the  galvanic  current  depends  on  its  den- 
sity. If  one  electrode  has  a  large  surface,  and  the 
other  a  very  small  surface,  the  current  lines  will 
be  distributed  through  a  con- 
siderable cross-section  in  the 
first  instance  and  converge  to  a 
small  cone  in  the  second.  The 
threshold  value  of  stimulation 
will  not  be  reached  at  the  large 
electrode,  and  stimulation  will 
occur  only  at  the  small  elec- 
trode. Thus  the  large  "indif- 
ferent" electrode  may  be  placed  on  any  part  of  the 
frog's  body,  and  the  convenient  small  electrode  be 
used  to  stimulate  the  heart. 

Cover  the  indifferent  electrode  (consisting  of  a 
brass  plate  furnished  with  a  binding  post)  with 
cotton  wet  with  saline  solution.  Make  one  fine- 
pointed  non-polarizable  electrode.  Connect  a 
dry  ceil  with  the  metre  posts  (0  and  1)  of  the 
rheocord  through  a  simple  key  (Fig.  19).  Con- 
nect  post    0    and   the    slider   through    a    pole- 


STIMULATION    OF   MUSCLE   AND   NERVE  75 

changer  (with  cross-wires)  with  the  electrodes. 
Expose  the  heart,  according  to  the  following 
method  :  Place  the  brainless  frog,  back  down,  in 
the  holder.  (Jut  through  the  skin  across  the 
middle  of  the  body  from  side  to  side.  Make  a 
second  cut  in  the  middle  line  from  the  first  cut 
to  near  the  lower  jaw.  Turn  back  the  Haps.  Cut 
through  the  sternal  cartilage  near  its  lower  end, 
thus  avoiding  the  epigastric  vein.  Cautiously 
remove  the  breast  bone,  doing  no  harm  to  deeper 
parts.  Open  the  delicate  membrane  (pericardium) 
which  surrounds  the  heart.  Tie  a  ligature  about 
the  auriculo-ventricular  junction,  to  stop  the  ven- 
tricular contractions.  Place  the  indifferent  elec- 
trode over  the  larynx  and  the  non-polarizable 
electrode  on  the  ventricle.  Turn  the  pole- 
changer  so  that  the  electrode  on  the  heart  be- 
comes the  anode.     Close  and  then  open  the  key. 

Contraction  will  take  place  on  opening  only, 
if  at  all.  Eeverse  the  pole-changer  so  that  the 
cardiac  electrode  becomes  the  cathode.  Close 
and  then  open  the  key. 

Contraction  takes  place  at  closure  only. 

Polar  Stimulation  of  Nerve 

Law  of  Contraction.  —  1.  Whether  contraction 
will  follow  the  galvanic  stimulation  of  a  motor 
nerve  depends  on  the   irritability  of   the  nerve 


76      THE   PHYSIOLOGY   OF   MUSCLE   AND   NEEVE 

and  the  direction  and  intensity  of  the  current. 
The  current  may  pass  through  the  intrapolar 
portion  of  the  nerve  towards  the  muscle  (de- 
scending current)  or  away  from  it  (ascending 
current).  The  intensity  may  be  weak,  medium, 
or  strong;  intensity  in  this  case  is  evidently 
merely  a  relative  term,  depending  on  the  irrita- 
bility of  the  particular  nerve  in  hand.  We  will 
test  first  the  effect  of  the  ascending  current. 


Fig.  20.1 


Connect  a  dry  cell  through  an  open  key  with 
the  metre  posts  of  the  rheocord  (Fig.  20).  Join 
the  positive  post  and  the  slider  through  a  pole- 
changer  (cross-wires  in  place),  with  the  non- 
polarizable  electrodes  placed  in  the  moist 
chamber  (Fig.  13,  page  60),  in  the  holders  farthest 
from  the  opening  for  the  muscle.  Make  a 
nerve-muscle  preparation.  Secure  the  femur  in 
the  femur  clamp  of  the  moist  chamber.     Let  the 

1  The  inductorium  shown  in  Fig.  20  is  not  used  in  this  ex- 
periment, but  in  the  first  experiment  on  page  79. 


STIMULATION    OF    MUSCLE    AND    NKKVK  77 

nerve  lie  on  the  non-polarizable  electrodes. 
Attach  the  Achilles  tendon  to  the  muscle  lever. 
Keep  the  ail  in   the   chamber    moist   by  lining 

the  glass  shade  with  filter  paper  saturated  with 
water.  Arrange  the  pole-changer  so  that  the 
anode  shall  be  next  the  muscle.  Move  the  slider 
near  the  positive  post.  Make  and  break  the  gal- 
vanic current.  If  no  contraction  is  secured, 
move  the  slider  to  increase  the  current,  and 
repeat  the  experiment. 

The  first  contraction  will  take  place  on  mak- 
ing the  current.  Continue  to  increase  the  cur- 
rent strength  by  moving  the  slider. 

A  point  will  be  reached  at  which  contraction 
will  occur  both  on  opening  and  closure. 

Increase  the  intensity  of  the  current  by  add- 
ing dry  cells  in  series  (zinc  to  carbon),  testing 
the  effect  after  each  addition  by  closing  and 
opening  the  current. 

An  intensity  will  be  reached  at  which  opening 
and  not  closure  causes  contraction. 

In  a  similar  manner,  work  out  the  law  of  con- 
traction for  descending  currents.  (It  may  be 
necessary  to  take  a  fresh  nerve-muscle  prepa- 
ration.) 

Set  down  the  results  in  a  table. 


Intensity 
of  current. 

V<irll. 

Make. 

ling  current. 
Break. 

Descending  current 
Make.                    Break. 

Weak. 

Contr. 

Rest. 

Contr. 

Rest. 

Mr. limn. 

Contr. 

Contr. 

Contr. 

Contr. 

Strong. 

Rest. 

Contr. 

Contr. 

Rest  (Weak  contr.). 

78      THE   PHYSIOLOGY   OF  MUSCLE   AND   NEKVE 

2.  The  remarkable  nature  of  these  results  is 
apparent  on  observing  that  contraction  is  easily 
secured  on  closing  a  weak  ascending  current  and 
yet  cannot  be  obtained  with  a  strong  one.  The 
first  step  in  the  inquiry  into  the  causes  of  the 
phenomena  is  to  determine  whether  the  stimu- 
lation is  polar.  That  the  nerve  impulse  really 
starts  at  the  cathode  on  closure  and  at  the  anode 
on  opening  is  shown  (1)  by  the  fact  that  the 
interval  between  stimulation  and  contraction, 
with  the  ascending  current,  in  which  the  anode 
is  next  the  muscle,  is  longer  at  closure  than  on 
opening,  while  the  opposite  is  the  case  when  the 
current  is  descending.  (2)  With  descending 
currents,  it  sometimes  happens  that  opening 
produces  tetanus  instead  of  a  simple  twitch. 
If  this  tetanus  appears,  the  student  should  sever 
the  nerve  between  the  electrodes.  Immediately 
the  contractions  will  cease.  They  must  there- 
fore have  arisen  at  the  anode,  for  the  cath- 
ode still  remains  in  full  connection  with  the 
muscle. 

Changes  in  Irritability.  —  The  second  step  in 
this  inquiry  is  to  determine  the  nature  of  the 
changes  at  the  poles.  For  this  purpose  the 
nerve  should  be  stimulated  in  the  cathodal  and 
anodal  regions  during  the  passage  of  the  constant 
current. 


STIMULATION   OF   MUSCLE   AND   NERVE         79 

1.  Place  ordinary  metal  electrodes  in  the  pair 
of  holders  next  the  muscle  in  the  moist  chamber. 
Connect  them  with  the  secondary  coil  of  an  in- 
ductoriuin  (Fig.  20).  Arrange  the  primary  for 
single  induction  shocks,  which  must  not  be  max- 
imal. Turn  the  pole-changer  to  bring  the  cathode 
next  the  metal  electrodes.  Using  a  break  induc- 
tion current  as  stimulus,  record  on  a  stationary 
drum  three  contractions,  (1)  before  the  passing  of 
the  galvanic  current  through  the  nerve,  (2)  dur- 
ing its  passage,  (3)  after  its  passage. 

The  second  contraction  —  that  obtained  by 
stimulating  in  the  cathodal  region  during  the 
passage  of  the  galvanic  current  —  will  be  greater 
than  the  other  two. 

Reverse  the  galvanic  current  and  repeat  the 
experiment,  the  stimulation  now  being  in  the 
anodal  region. 

The  stimulation  in  the  anodal  region  during 
the  passage  of  the  galvanic  current  causes  less 
than  the  normal  contraction. 

2.  The  stimulating  current  may  be  superposed 
directly  on  the  polarizing  current  by  using  the 
same  electrodes. 

Connect  a  dry  cell  through  an  open  key  with 
the  0  and  1  metre  posts  of  the  rheocord 
( Fig.  21).  Connect  the  positive  post  of  the 
rheocord  with  one  of  the  non-polarizable  elec- 


80   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

trodes.  Join  the  slider  to  one  end  of  the  second- 
ary wire  of  an  inductorium ;  to  the  other  end  join 
the  remaining  non-polarizable  electrode.  If  the 
positive  pole  of  the  secondary  coil  is  not  known, 
determine  it  by  the  electrolytic  method  (pages  27 
and  119  .  Arrange  the  primary  coil  of  the  induc- 
torium for  single  submaximal  induction  currents. 
Make  and  break  the  induction  current,  and  record 
the  contractions  on  the  drum.     Xow  pass  a  weak 

polarizing  current 
through  the  nerve 
and  stimulate  again 
with  the  induction 
current. 

It  will  be  found 
that  the  stimulating 
effect  of  the  induc- 
tion current  is  increased  when  the  direction  of 
the  induction  current  coincides  with  that  of  the 
polarizing  current,  i.  e.  when  the  cathode  (which 
is  the  sole  source  of  the  induction  stimulus,  as 
pointed  out  on  page  121)  coincides  with  the  cath- 
ode of  the  polarizing  current.  "When  the  cathode 
of  the  induction  circuit  falls  in  the  anodal  region 
of  the  polarizing  circuit,  the  stimulating  effect  is 
diminished.  Very  strong  polarizing  currents 
produce  such  alterations  in  irritability  that  the 
additional   alteration    caused    by   the    brief    in- 


STIMULATION    OF   MUSCLE    AND   NERVE         81 

duction   current   is    not   great  enough   to   be  a 
stimulus. 

The  law  revealed  by  this  experiment  may  be 
thus  expressed.  The  same  stimulating  current 
has  a  greater  stimulating  effect  when  it  coincides 
in  direction  with  a  pre-existing  current,  and  a 
lessened  effect  when  it  is  opposed  in  direction  to 
a  pre-existing  current.  This  law  explains  the 
interference  observed  between  stimulating  cur- 
rents and  demarcation  or  injury  currents  of  nerve 
and  muscle  (see  page  155). 

3.  Place  a  drop  of  saturated  solution  of  sodium 
chloride  on  the  nerve  in  the  extrapolar  region 
near  one  of  the  non-polarizable  elect: 
Eecord  the  irregular  tetanus  (chemical  stimula- 
tion) on  a  slowly  moving  drum.  Make  the  polar- 
izing current. 

Note  that  the  tetanus  is  increased  when  the 
cathode  is  nearer  the  stimulating  solution,  but 
diminished  when  the  anode  is  nearer. 

Hence  the  irritability  of  the  nerve  is  altered 
during  the  passage  of  the  electric  current 
trotonus)  ;  *  it  is   increased  in  the  neighborhood 

1  The  change  in  the  excitability  of  the  nerve  produ . 
the  electric  current  is  so  generally  called  electrotonus  that  the 
term  cannot  well  be  changed.  It  should  not  be  confused  with 
the  electrotonus  described  on  page  ISO,  though  it  is  possible 
that  the  two  phenomena  have  a  similar  if  not  identical  first 
cause. 

6 


82   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

of  the  cathode  (catelectrotonus)  and  is  diminished 
in  the  neighborhood  of  the  anode  (anelectro- 
tonus).  In  the  intrapolar  region,  the  cathodal 
touches  the  anodal  area  at  the  so-called  indifferent 
point.  This  point  approaches  the  cathode  when 
the  intensity  of  the  polarizing  current  is  increased. 

The  greater  the  length  of  nerve  between  the 
electrodes,  the  greater  the  extrapolar  electrotonus. 
Catelectrotonus  rises  rapidly  to  a  maximum  as 
soon  as  the  circuit  is  closed,  and  then  gradually 
wanes.  Anelectrotonus  develops  more  slowly  and 
does  not  reach  its  maximum  for  some  time  after 
closure. 

On  the  opening  of  the  circuit,  the  conditions  at 
the  anode  and  cathode  are  reversed,  the  irritability 
falls  at  the  cathode  and  rises  at  the  anode.  The 
fall  in  the  cathodal  region  is  of  short  duration, 
and  the  irritability  soon  returns  again  towards 
normal.  In  the  anodal  region,  the  rise  on  open- 
ing is  unbroken. 

Changes  in  Conductivity.  —  We  have  seen 
that  the  irritability  is  altered  by  the  galvanic 
current.     The  conductivity  also  is  altered. 

Connect  a  dry  cell  through  a  pole-changer  with 
cross-wires  to  a  pair  of  non-polarizable  electrodes 
placed  in  the  holders  of  the  moist  chamber 
farthest  from  the  muscle  (Fig.  22).  Leave  one 
wire    uncoupled    until  the    current    is   wanted. 


STIMULATION    OF   MUSCLE    AND    NERVE         83 


Connect  another  cell  with  the  primary  coil  of 
the  inductorium  arranged  for  break  induction 
shocks,  placing  in  the  circuit  a  simple  key  and 
the  electromagnetic  signal.  Lead  wires  from  the 
poles  of  the  secondary  coil  to  the  side  cups  of  a 
pole-changer  (without  cross-wires).  In  each  of 
the  remaining  two  holders  of  the  moist  chamber 
place  a  cork  pierced 
by  two  metal  elec- 
trodes. One  wire  in 
each  pair  should  be 
insulated  from  its  fel- 
low by  rubber  tubing 
drawn  over  the  part 
between  the  cork  and 
the  end  of  the  elec- 
trode to  be  applied  to 
the  nerve.  Connect 
the   wire    soldered    to 

the  basal  ends  of  these  electrodes  with  the  re- 
maining cups  of  the  pole-changer  in  the  second- 
ary circuit  of  the  inductorium.  Arrange  the 
signal  to  write  on  the  smoked  drum  beneath  the 
writing  point  of  the  muscle  lever. 

Make  a  nerve-muscle  preparation.  Let  the 
nerve  rest  on  the  non-polarizable  electrodes  near 
the  cross-section.  Place  one  pair  of  the  metal 
electrodes  beneath  the  nerve  near  the  muscle,  the 


Fig.  22. 


84      THE   PHYSIOLOGY   OF   MUSCLE   AND   NEKVE 

other  pair  near  the  non-polarizable  electrodes. 
The  clock-work  of  the  drum  should  be  fully- 
wound  (not  over-wound),  and  the  drum  should 
revolve  at  its  most  rapid  speed.  Write  two 
muscle  curves.  For  the  first  stimulate  through 
the  metal  electrodes  nearer  the  muscle ;  for  the 
second  through  the  metal  electrodes  farther  from 
the  muscle. 

"While  each  curve  is  writing,  let  a  tuning  fork 
record  its  vibrations  beneath  the  point  of  the 
muscle  lever.  To  mark  on  the  abscissa  of  the 
muscle  curve  the  exact  moment  at  which  the 
muscle  was  stimulated,  turn  back  the  drum  until 
the  writing  point  of  the  signal  lies  precisely  in 
the  line  described  by  it  when  the  current  was 
broken.  Now  stimulate  the  muscle  with  another 
induction  shock.  The  curved  ordinate  of  the 
muscle  lever  will  be  synchronous  with  the  ordi- 
nate of  the  signal. 

The  interval  between  the  moment  of  stimula- 
tion, as  recorded  by  the  signal,  and  the  beginning 
of  contraction,  is  greater  when  the  nerve  is  stim- 
ulated far  from  the  muscle.  The  difference  is 
the  time  required  for  the  nerve  impulse  to  tra- 
verse the  length  of  nerve  between  the  electrodes, 
provided  of  course  that  the  interval  between  the 
arrival  of  the  nerve  impulse  in  the  muscle  and 
the  beginning  of  the  contraction  is  the  same  in 


STIMULATION   OF   MUSCLE   AND   NERVE         85 

both  cases,  an  assumption  considered  reasonable 
by  most  physiologists. 

Write  now  three  other  pairs  of  curves  ;  one 
while  a  galvanic  current  passes  through  the  non- 
polarizable  electrodes  in  a  descending  direction 
(cathode  nearer  the  muscle)  ;  a  second  while  an 
ascending  current  passes  (anode  nearer  the  mus- 
cle) ;  and  a  third,  after  the  galvanic  current  has 
been  some  minutes  broken,  as  a  control.  During 
the  writing  of  these  curves  measure  the  velocity 
of  the  drum  with  the  tuning  fork  as  before. 

The  speed  of  the  nerve  impulse  will  be  found 
to  be  greater  than  normal  when  the  nerve  im- 
pulse starting  at  the  second  pair  of  metal  elec- 
trodes passes  through  an  extrapolar  cathodal 
area  (i.  c.  stimulation  during  descending  current), 
and  less  than  normal  when  that  region  is  made 
anodal  by  reversing  the  galvanic  current.  In 
other  words,  the  conductivity  of  the  nerve  has 
been  increased  by  cathodal  and  diminished  by 
anodal  stimulation. 

2.  Conductivity  is  diminished  by  strong  or  pro- 
tracted current*  in  the  cathodal  as  well  as  in  the 
anodal  region.  —  Place  two  non-polarizable  elec- 
trodes upon  the  nerve  about  3  cm.  apart.  Con- 
nect them  through  a  pole-changer  with  two  dry 
cells  (Fig.  23).  In  the  middle  of  the  intrapolai 
region    place    two   stimulating    electrodes    close 


86     THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

together.  Connect  one  of  the  stimulating  elec- 
trodes directly  to  the  secondary  coil  of  an  induc- 
torium  arranged  for  single  induction  currents. 
Lead  from  the  other  stimulating  electrode  to. a 
piece  of  nerve  or  muscle  about  4  cm.  long,  and 
thence  to  the  secondary  coil.  The  introduction 
of  this  great  resistance  will  keep  most  of  the 
polarizing  current  in  the  short  bridge  of  nerve 
between  the  polarizing  electrodes.     Without  this 

resistance,    the    polariz- 
X^~@\  *n&  current  would  pass 

\  J  through  the  stimulating 

\M?  circuit  in  preference  to 

crossing  the   nerve   be- 
tween   the    stimulating 


-Uo= 


electrodes.    Observe  that 
l — OcT  s^o)    the  nerve  impulse   ere- 

^  ated    by    the    stimulus 

Fig.  23.  J 

must  pass  through  the 
cathodal  region,  if  the  current  be  descending,  or 
the  anodal  region,  if  the  current  be  ascending, 
in  order  to  reach  the  muscle. 

Find  the  position  of  the  secondary  coil  at 
which  the  muscle  will  barely  contract  on  making 
the  stimulating  current.  Turn  the  pole-changer 
to  bring  the  anode  between  the  stimulating  elec- 
trodes and  the  muscle,  and  make  the  polar- 
izing   current.      Open    the    polarizing    current. 


STIMULATION    OF   MUSCLE    AND   NERVE  87 

After  a  three-minute  interval  of  rest,  turn  the 
pole-changer  to  bring  the  cathode  next  the  mus- 
cle and  make  the  polarizing  current.  It  should 
be  allowed  to  How  as  long  as  before.  Then 
stimulate  again  with  a  make  induction  current 
'of  the  same  intensity  as  before. 

Contraction  will  be  absent,  or  at  most  very- 
weak.  The  impulse  will  be  blocked  in  the 
cathodal  region.  In  truth,  during  the  passage  of 
strong  or  protracted  currents,  the  conductivity  is 
more  diminished  in  the  cathodal  than  in  the 
anodal  region. 

Griitzner  and  Tigerstedt  believe  that  the  open- 
ing contraction  is  due  to  the  stimulation  of  the 
nerve  or  muscle  by  the  polarization  current 
which  appears  when  the  galvanic  current  is 
broken.  The  polarization  current  may  be  said 
to  be  closed  when  the  galvanic  current  is  opened. 
These  observers,  therefore,  hold  that  stimulation 
takes  place  only  at  closure. 

We  are  now  in  a  position  to  account  for  the 
phenomena  described  by  the  law  of  contraction. 
The  irritability  of  the  nerve  is  increased  at  the 
cathode  on  closure,  and  at  the  anode  on  opening 
the  galvanic  current.  This  rise  of  irritability 
stimulates  the  nerve.  The  rise  at  the  cathode  is 
a  more  effective  stimulus  than  the  rise  at  the 
anode ;  consequently  with  weak  currents  the  first 


88      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

stimulus  to  produce  contraction  is  cathodal,  i.  e. 
at  the  closure  of  the  circuit.  As  the  current  in- 
tensity is  increased,  the  anodal  rise  becomes  also 
effective,  and  contraction  is  secured  by  both  mak- 
ing and  breaking  the  current. 

But  we  have  to  deal  also  with  a  decrease  in  irri- 
tability, and,  still  more  important  for  the  expla- 
nation of  the  effects  of  strong  currents,  with  a 
decrease  in  conductivity.  The  irritability  and  con- 
ductivity are  decreased  on  closure  at  the  anode 
and  on  opening  at  the  cathoda  If  the  anode 
is  next  the  muscle  (Fig.  24),  the 
* c  decrease  in  conductivity  on  clos- 
ure of  a  strong  current  will  block 
'«— *  the  nerve  impulse  coming  from 
„    n„  the    cathode :    it    will    therefore 

Fig.  24.  ' 

never  reach  the  muscle,  and  there 
will  be  no  contraction  on  closure.  If  the  cathode 
is  next  the  muscle,  the  conductivity  may  be  so 
decreased  on  opening  that  the  nerve  impulse 
coming  from  the  anode  may  be  blocked.  The 
decrease  at  cathode,  when  the  current  is  broken, 
is,  however,  less  marked  than  the  decrease  at 
anode  when  the  current  is  made,  so  that  the 
cathodal  decrease,  even  with  strong  currents, 
sometimes  fails  to  block  the  impulse  entirely. 
In  that  case,  a  weak  contraction  may  be  obtained 
at  the  break  of  the  descending  current. 


stimulation  of  muscle  and  nerve      89 

Stimulation  of  Human  Nerves 

Duchenne  devised  a  method  by  which  either  the 
motor  or  the  sensory  human  nerves  can  be  stimu- 
lated at  will,  and  the  reaction  of  single  muscles 
or  groups  of  muscles  to  electricity  determined. 
When  electrodes  are  placed  on  the  surface  of  the 
skin  and  the  circuit  is  made,  the  current  entering 
at  the  anode  will  spread  in  current  lines  through 
the  entire  body.  At  the  cathode,  all  these  lines 
will  converge  again.  The  density  of  the  current 
depends  on  the  concentration  of  the  current 
lines.  Thus  the  density  is  relatively  great  at 
the  electrodes,  and  becomes  rapidly  weaker  as 
the  lines  diverge  between  them.  The  smaller  the 
electrode,  the  greater  the  density.  The  stimulat- 
ing effect  depends  on  the  density.  With  small 
electrodes,  a  current  not  sufficient  to  cause  stimu- 
lation may  gradually  be  increased  in  strength 
until  the  density  at  the  electrode  becomes  great 
enough  to  stimulate,  while  in  all  other  regions  it 
is  not  yet  great  enough.  Thus  a  local  stimula- 
tion is  secured.  But  this  local  stimulus  does 
not  sufficiently  distinguish  between  the  sensory 
nerves  and  the  motor  nerves  and  muscles  ;  for  in 
order  to  reach  the  deeper  lying  motor  nerves  and 
muscles,  the  current  must  pass  through  the  skin. 
The  resistance  of  the  epidermis  is  very  great,  and 


90      THE   PHYSIOLOGY   OF   MUSCLE   AND   NEKVE 

currents  of  considerable  intensity  are  necessary 
to  overcome  it.  Once  through  the  epidermis,  the 
current  spreads  immediately  in  all  directions 
through  the  cutis,  where  it  stimulates  the  very 

Mm.  lumbricales 


M.  opponens  digit,  min. 

M.  flexor  digit,  min. 

M.  abd.  digit,  min. 

M.  palmaris  brevis 

N.    ulnaris   (ram.  vol. 
prof.) 

N.  medianus 

M.    flexor   digit,    subl. 
(ind.  and  minim.) 

M.  flexor,   digit,    subl. 
(II  &  III) 


M.  flexor  digit  profund. 

M.    ulnaris      internus 

(flexor  carp,  uln.) 

M.  palm,  longus 

M.  pronator  teres 

N.  medianus 


M.  adductor  poll. 
M.  flexor  poll,  brevis 
M.  opponens  poilicis 
M.  abductor  poll,  brevis 


M.  flexor  poilicis  longus 


—  M.  flexor  digit,  subl. 


M.  rad.  internus  (flexor 
carp,  rad.) 


M.  supin.  longus 


Fig.  25.    The  motor  points  on  the  anterior  surface  of  the  forearm  and 
hand. 


numerous  sensory  nerves.  When  the  muscles  or 
motor  nerves  are  reached,  the  density  is  much 
reduced,  and  may  not  suffice  for  stimulation. 
Thus  the  result  may  be  not  motor  stimulation, 
but  simply  pain  from  stimulation  of  the  sensory 


STIMULATION    OF    MUSCLE   ANI>   NERVE 


01 


nerves.     For   painless    motor   stimulation   it   is, 
therefore,  necessary    to  increase  the  strength  of 

the  current  which  reaches   the    muscle  or  motor 
nerve  and  to  diminish  the  density  of  the  current 


M.  InterosB.  dors.  IV 
M,  abd.  digit,  min. 


51.  ext.  indicia  propr. 
M.  ulnaris  extern. 

M.  rod.  ext.  brevis 


M.  ext.  pollicis  longus 
M.  ext.  indicia  propr. 


M.  ext.  dig.  min.  propr. 
M.  ext.  dig.  communis 


M.  supin.  brevis 


M.  rad.  ext.  longus  - 
M.  supin.  longus  - 


Fig.  26.    The  motor-points  on  the  posterior  surface  of  the  forearm  and 
hand. 


at  the  electrodes.  These  ends  are  accomplished 
by  using  for  electrodes  large  metal  plates  cov- 
ered with  sponge  or  cotton  wTet  with  saline  solu- 
tion. The  liquid  diminishes  greatly  the  resistance 
of  the   epidermis,  so  that  more   current  reaches 


92   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

the  deeper  tissues ;  and  the  large  surface  offers  a 
broad  path  for  the  current,  so  that  the  current  lines 
are  not  so  concentrated  as  to  stimulate  painfully 
the  sensory  nerves  of  the  cutis.  One  sponge  elec- 
trode may  be  made  considerably  smaller  than  the 
other  without  forfeiting  this  advantage,  while  the 
smaller  size  makes  it  easier  to  localize  the  stimulus. 

Muscles  are  best  stimulated  through  their 
nerves,  for  two  reasons :  the  nerve  responds  to 
a  weaker  stimulus  than  the  muscle ;  and, 
secondly,  it  is  much  easier  to  secure  contraction 
of  the  whole  muscle  by  stimulating  the  nerve 
than  by  attempting  to  pass  a  current  through  the 
muscle  directly.  The  smaller  electrode  should 
be  placed  over  the  nerve,  the  larger  on  some  in- 
different region.  The  indifferent  electrode  may 
be  placed  over  the  muscle  itself,  if  it  is  important 
that  the  resistance  shall  not  be  increased  by  the 
too  great  separation  of  the  electrodes. 

Duchenne  found  that  certain  points  were  es- 
pecially favorable  for  the  stimulation  of  indi- 
vidual muscles.  Eemak  discovered  that  these 
"  motor  points  "  were  simply  the  places  at  which 
the  nerves  entered  the  muscle.  The  motor  points 
of  the  forearm  are  shown  in  Figs.  25  and  26. 

Stimulation  of  Motor  Points.  —  Arrange  the 
inductorium  for  single  induction  shocks.  De- 
termine by  the  electrolytic  method  which  pole 


STIMULATION   OF   MUSCLE   AND    NERVE         93 

of  the  secondary  coil  is  the  cathode  when  the 
primary  current  is  broken  (pages  27  and  119). 
To  this  pole  connect  the  small  (stimulating) 
electrode  ;  to  the  other  pole  connect  the  large 
(indifferent)  electrode.  Place  the  indifferent 
electrode  on  the  arm  or  neck.  With  the  small 
electrode  make  out  the  motor  points  indicated  in 
Figs.  25  and  26. 

Polar  Stimulation  of  Human  Nerves.  —  In  the 
hands  of  the  earlier  observers  the  stimulation 
of  nerves  within  the  body  gave  results  often 
contrary  to  the  law  of  polar  stimulation  so  easily 
demonstrated  in  extirpated  nerves.  The  ex- 
planation of  these  inconstant  results  lay  in  the 
failure  to  comprehend  the  distinction  between 
the  stimulating  positive  and  negative  electrodes 
and  the  physiological  anode  and  cathode  (com- 
pare page  71).  Even  when  the  monopolar  method 
is  employed,  and  a  small  electrode  is  brought  as 
near  as  possible  to  the  nerve  to  be  stimulated, 
while  a  large  indifferent  electrode  is  placed  on 
some  other  part  of  the  body,  it  is 

impossible  to  secure  true  mono-     . — JU L_^ 

polar  stimulation.  The  current  cccccc  aXaaaX 
entering  at  the  anode  does  not  „    0_ 

o  Fig.  27. 

remain    in    the    nerve,  but  very 

soon   passes   out    into    the   surrounding   tissues 

(Fig.  27).      Hence  there  are  physiological  cath- 


94      THE   PHYSIOLOGY  OF  MUSCLE   AND   NEKVE 

odes  on  both  sides  of  the  positive  electrode,  and 
for  the  like  reason  physiological  anodes  on  both 
sides  of  the  negative  electrode.  Thus  both 
anodal  and  cathodal  stimulation  take  place, 
whichever  electrode  rests  over  the  nerve.  It 
is  therefore  incorrect  to  speak  of  ascending 
and  descending  currents  in  the  case  of  nerves 
stimulated  in  situ.  It  should  be  pointed  out 
too,  that  the  density  of  the  current  is  greater  on 
the  side  of  the  nerve  nearer  the  electrode  than 
on  the  more  deeply  placed  side  cut  by  current 
lines  already  rapidly  diverging. 

With  these  facts  in  mind,  we  may  compare 
the  polar  stimulation  of  human  nerve  with  the 
law  already  determined  for  the  isolated  nerves 
of  the  frog  (page  77). 

Connect  8  dry  cells  in  series  (the  carbon  of 
one  cell  to  the  zinc  of  the  next,  etc.).  Coupling 
in  this  way  enables  the  electromotive  force  of 
each  cell  to  be  added  with  slight  loss  to  that  of 
the  others,  provided  the  resistance  in  the  circuit 
outside  the  cells  is  so  great  that  the  internal 
resistance  of  the  battery  disappears  in  compari- 
son, as  is  the  case  where  living  tissues  form  part 
of  the  circuit.  Connect  the  terminal  zinc  and 
carbon  pole  through  a  pole-changer  (with  cross- 
wires)  to  a  small  and  a  large  electrode  covered 
with  cotton  thoroughly  wet  with  strong  saline 


STIMULATION    OF   MUSCLE    AND    NERVE  95 

solution.  Place  the  small  electrode  over  the 
ulnar  nerve  between  the  internal  condyle  and 
the  olecranon,  a  little  above  the  furrow.  Make 
and  break  the  current,  If  no  contraction  is 
secured,  add  cells  to  the  battery  until  contraction 
occurs. 

It  will  be  found  that  the  first  contraction 
occurs  on  closure  with  the  cathode  over  the 
nerve.  With  this  strength  of  current  the  opening 
contraction  will  be  absent. 

Turn  the  pole-changer  so  as  to  bring  the  anode 
over  the  nerve  and  increase  the  intensity  still 
further. 

A  strength  will  be  reached  at  which  closure 
with  the  anode  over  the  nerve  will  cause  contrac- 
tion, but  the  opening  of  the  current  will  still  be 
without  effect.  A  slightly  greater  intensity  will 
now  bring  out  the  anodal  opening  contraction.1 

In  the  mean  time  the  cathodal  closing  con- 
traction has  increased  in  force  with  each  addition 
to  the  intensity  of  the  current.  With 'about  18 
cells,  the  muscle  twitch  on  closure  may  give 
place  to  a  continued  contraction  or  tetanus,  the 
cathodal  closing  tetanus.     Further  increase  gives 

1  Sometimes  anodal  opening  contraction  precedes  the  closing 
contraction.  This  inconstancy  results  from  variations  in  cur- 
rent strength  due  to  differences  in  the  tissues  surrounding  tho 
nerve. 


96      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

*■ 
cathodal  opening   contraction,  and   finally  very- 
strong  currents  sometimes  cause  anodal  closing 
tetanus.     Thus  we  have 

1.  Cathodal  closing  contraction. 

2.  Anodal  closing  contraction. 

3.  Anodal  opening  contraction. 

4.  Cathodal  closing  tetanus. 

5.  Cathodal  opening  contraction. 

6.  Anodal  closing  tetanus  (rare). 
Sometimes   the  anodal  opening   precedes   the 

anodal  closing  contraction. 

The  apparent  deviation  from  the  law  of  polar 
excitation  (cathodal  on  closure,  anodal  on  open- 
ing) is  explained  by  the  presence  of  a  physi- 
ological anode  and  cathode  at  each  electrode, 
as  already  mentioned.  The  appearance  of  cath- 
odal closing  contraction  before  anodal  closing 
contraction  is  due  to  the  fact  that  when  the 
negative  electrode  lies  over  the  nerve  the  physi- 
ological cathode  will  be  found  on  the  side  of  the 
nerve  next  the  electrode.  The  nearer  the  elec- 
trode, the  greater  the  current  density,  and  hence 
the  earlier  the  threshold  value  is  reached.  When, 
however,  the  positive  electrode  lies  over  the 
nerve,  the  physiological  cathode  will  be  found 
on  the  side  of  the  nerve  farther  from  the  elec- 
trode, where  the  density  is  less,  owing  to  the 
divergence  of  the  current  lines.     The  threshold 


STIMULATION   OF   MUSCLE   AND   NERVE  91 

value  will  be  reached  first  at  the  point  of  higher 
density,  and  consequently  the  first  contraction 
will  appear  while  the  negative  electrode  rests 
over  the  nerve.  The  anodal  opening  contraction 
appears  before  the  cathodal  opening  contraction 
for  a  similar  reason. 

Reaction  of  Degeneration.  —  Whenever  a  nerve 
is  severed,  the  portion  separated  from  the  cell  of 
origin  of  the  nerve  "  degenerates."  The  degener- 
ation does  not  begin  at  the  section  and  advance 
to  the  terminal  branches,  but  takes  place  al- 
most or  quite  simultaneously  throughout  the 
nerve.  Eanvier  states  that  it  begins  first  in  the 
end  plates.  Severed  nerves  in  the  brain  and 
spinal  cord  degenerate  in  the  same  way,  and  this 
"  Wallerian  degeneration "  (Waller,  1850)  is  a 
valuable  aid  in  tracing  the  path  of  nerve  fibres 
in  the  central  nervous  system.  Degeneration  is 
accompanied  by  changes  in  the  reaction  to  the 
electric  current  which  form  a  valuable  aid  in  the 
diagnosis  of  the  seat  of  the  lesion  in  cases  of 
paralysis.  The  muscle  reacts  imperfectly,  or  not 
at  all,  to  the  brief  induction  current,  while  its 
reaction  to  the  long  galvanic  current  may  even 
be  greater  than  usual. 

Expose  each  gastrocnemius  muscle  in  a  frog, 
the  left  sciatic  nerve  of  which  has  been  severed 
ten  days  before  this  experiment.  Stimulate  each 
7 


98      THE   PHYSIOLOGY    OF   MUSCLE   AND   NEKVE 

muscle  with  weak  induction  currents  and  with 
the  galvanic  current. 

The  muscle,  the  nerves  of  which  are  degen- 
erated, reacts  more  readily  to  the  galvanic  current 
than  to  the  brief  induction  current.  The  normal 
muscle  shows  the  opposite  reaction. 

In  man,  the  reaction  of  degeneration  in  the 
case  of  muscle  consists  of  a  lessened  or  lost 
excitability  to  the  induced  current  with  increased 
excitability  to  the  galvanic  current.  The  duration 
of  contraction  may  be  greater  than  normal.  In 
polar  stimulation,  anodal  closing  contraction  may 
appear  before  cathodal  closing  contraction,  —  a 
reversal  of  the  normal  sequence. 

In  degenerated  nerve  there  is  of  course  a  total 
loss  of  irritability,  corresponding  to  the  destruc- 
tion of  the  axis  cylinder. 

Galvanoteopism 

Paramecium.  —  Connect  two  non-polarizable 
electrodes  through  an  open  key  with  a  dry  cell. 
On  a  glass  microscope-slide  make  with  normal 
saline  clay  an  enclosure  about  one  centimetre 
square  and  a  few  millimetres  high.  Place  in 
this  a  little  hay  infusion  containing  Paramecia. 
Bring  non-polarizable  electrodes  against  two  op- 
posite sides  of  the  clay  cell.  Examine  the  infu- 
sion with  a  very  low  power.     Close  the  key. 


STIMULATION    OF    MUSCLE    AND   NERVE  99 

Upon  closure  each  Paramecium  turns  the  an- 
terior end  of  the  body  towards  the  cathode  and 
swims  in  that  direction.  In  a  very  short  time 
the  anodal  region  is  free,  and  the  Paramecia  are 
gathered  at  the  cathode,  where  they  remain  so 
long  as  the  current  flows. 

Open  the  key. 

The  Paramecia  now  turn  to  the  anode  and 
swim  in  that  direction,  but  the  anodal  grouping 
is  less  complete  than  the  cathodal,  and  lasts  but 
a  short  time.  Careful  observation  shows  that 
in  Paramecium  the  galvanic  reaction  consists  in 
placing  the  long  axis  of  the  body  in  the  current 
lines.  The  outermost  individuals  in  the  liquid 
will  therefore  describe  a  curve  corresponding  to 
the  curved  outer  current  lines. 

All  protozoa  and  many  other  animals  (for  ex- 
ample, the  tadpole  and  the  crayfish)  show  gal- 
vanotropism,  but  in  some,  movement  on  closure 
is  toward  the  positive  pole  (positive  galvano- 
tropism). 

These  experiments  on  skeletal,  smooth,  and 
cardiac  muscle,  on  nerve,  and  on  infusoria,  sug- 
gest that  polar  excitation  occurs  wherever  a  gal- 
vanic current  passes  through  irritable  tissue. 
Further  experience  would  confirm  this  view.  "We 
have  seen  that  the  changes  at  the  cathode  when 


100      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

the  current  is  made  are  not  momentary,  as  re- 
quired by  trie  hypothesis  of  DuBois-Eeymond, 
but  continue  so  long  as  the  current  flows.  This 
fact  appears  still  more  clearly  when  the  influence 
of  the  duration  of  the  current  is  examined. 

Influence  of  Duration  of  Stimulus 

1.  Smoke  a  drum.  Arrange  a  muscle  lever  to 
write  on  the  smoked  paper.  Prepare  non-polar- 
izable  electrodes  and  fasten  them  on  the  glass 
plate  of  the  nerve  holder. 
Arrange  the  inductorium 
for  maximal  induction 
currents.  Lead  from  the 
secondary  coil  to  a  pair  of 
the  end  cups  of  the  pole- 
changer  (without  cross- 
wires),  as  in  Fig.  28.  To 
the  opposite  cups  of  the  pole-changer  bring 
wires  from  a  dry  cell.  Connect  the  remaining 
cups  with  the  non-polarizable  electrodes.  Turn 
the  rocker  towards  the  induction  coil.  Fasten 
the  pelvic  attachment  of  the  curarized  sartorius  in 
the  muscle  clamp.  Tie  a  thread  to  the  fragment 
of  tibia,  and  fasten  the  thread  to  the  upright  pin 
of  the  muscle  lever,  so  that  the  horizontal  muscle 
shall  record  its  contraction  on  the  drum.  Start 
the  drum   at  moderate  speed.     Eecord   contrac- 


STIMULATION   OF   MUSCLE   AND   NEKVE        101 

tions  (1)  witli  maximal  break  shocks,  (2)  with 
closure  of  galvanic  current.    Compare  the  curves. 

The  curve  from  galvanic  stimulation  will  be  of 
greater  height  and  duration,  and  the  summit  of 
the  curve  will  be  less  pointed,  indicating  that 
the  muscle  remains  longer  in  the  stage  of  ex- 
treme shortening. 

Other  evidence  that  the  duration  of  the  stimu- 
lus modifies  the  character  of  the  contraction  is 
afforded  by  the  following  experiments  :  — 

2.  Make  two  cuts,  5  mm.  apart,  through  the 
frog's  stomach  at  right  angles  to  the  long  axis. 
Hang  the  ring  thus  secured  over  a  hook  clamped 
in  the  muscle  clamp.  Pass  a  bent  hook  through 
the  lower  end  of  the  ring,  and  attach  it  by  means 
of  a  fine  copper  wire  to  the  hook  on  the  muscle 
lever.  Carry  the  end  of  the  copper  wire  to  the 
binding  post  on  the  muscle  lever. 

Stimulate  with  single  induction  currents  of  a 
strength  about  the  threshold  value  for  skeletal 
muscle  of  frog. 

There  will  be  no  contraction. 

Stimulate  with  galvanic  current  (two  dry  cells), 
writing  three  curves,  the  duration  of  closure  be- 
ing approximately  one-fifth  second,  one,  and  five 
seconds,  respectively.     Compare  the  curves. 

The  maximum  shortening  with  currents  of 
brief  duration  Q  second)  is  very  much  less  than 


102      THE   PHYSIOLOGY  OF   MUSCLE   AND   NERVE 

with  currents  of  three  or  four  seconds  or  over. 
The  briefer  the  current  also,  the  quicker  will  the 
maximum  shortening  be  reached,  and  the  quicker 
will  be  the  relaxation. 

3.  If  the  galvanic  current  is  very  rapidly  made 
and  broken,  the  muscle  will  not  contract. 

The  same  is  true  of  the  ureter  (Engelmann). 

4.  Tonic  Contraction.  —  Examine  the  contrac- 
tion curve  already  recorded  by  the  smooth 
muscle  of  the  frog's  stomach.  Note  that  the 
muscle  remains  contracted  during  the  passage 
of  the  current.  The  curves  secured  from  the 
curarized  sartorius  (page  100)  also  show  this, 
but  to  a  much  less  degree  ;  the  sartorius  does 
not  resume  its  former  length  after  the  twitch  or 
closure  of  the  galvanic  current,  but  remains  con- 
tracted to  a  slight  extent.  This  tonic  contrac- 
tion appears  much  more  plainly  in  fatigued 
muscles. 

Fatigue  a  sartorius  muscle  by  stimulating  it 
with  a  galvanic  current  repeatedly  made  and 
broken.  After  a  time,  the  twitch  on  closure  will 
become  very  feeble,  and  finally  will  disappear, 
while  the  tonic  shortening  during  the  passage  of 
the  current  is  still  very  evident. 

5.  The  influence  of  duration  is  shown  also  in 
the  opening  contraction. 

Fasten  the  pelvic  attachment  of  a  sartorius 


STIMULATION   OF   MUSCLE   AND   NERVE        103 

muscle  in  the  muscle  clamp  and  connect  the 
other  end  with  the  upright  pin  of  the  muscle 
lever,  so  that  the  horizontal  muscle  shall  record 
its  contraction  on  a  drum.  Place  the  non-polar- 
izable  electrodes  on  the  ends  of  the  muscle. 
Allow  the  galvanic  current  from  a  dry  cell  to 
pass  through  the  muscle  until  the  closure  tonic 
contraction  has  disappeared,  then  open  the  key. 
Neglect  the  opening  twitch. 

The  muscle  will  not  return  to  its  original 
length,  but  will  remain  contracted  for  a  time 
(opening  tonic  contraction). 

Close  the  key  again. 

The  tonic  contraction  will  disappear. 

The  galvanic  current  in  this  case  checks  (in- 
hibits) a  contraction.  This  new  action  is  dis- 
cussed on  page  114. 

6.  Rhythmic  Contraction.  —  That  the  galvanic 
current  acts  as  a  stimulus  so  long  as  it  continues 
to  flow  is  shown  also  hy  the  fact  that  its  passage 
through  contractile  tissue  may  cause  the  muscle 
to  fall  into  rhythmic  contractions.  These  are 
easy  to  produce  in  muscles  which  normally  con- 
tract in  rhythms,  for  example,  the  heart ;  but 
they  may  under  some  circumstances  be  observed 
also  in  smooth  muscle,  and  even  in  skeletal 
muscles. 

Connect  a  dry  cell  through  a  simple  key  with 


104      THE   PHYSIOLOGY   OF   MUSCLE   AND   NEKVE 

the  metre  posts  of  the  rheocord.  Join  the  non- 
polarizable  electrodes  to  the  positive  post  and  the 
slider.  Bring  the  slider  against  the  positive  post, 
so  that  no  current  shall  flow  through  the  elec- 
trodes when  they  are  joined  by  the  tissue. 

Expose  the  heart.  Divide  the  ventricle  trans- 
versely near  its  base.  Lay  this  "  apex  "  prepara- 
tion on  a  glass  plate.  Keep  the  tissue  moistened 
with  normal  saline  solution,  but  avoid  excess. 
Bring  the  non-polarizable  electrodes  against  the 
two  sides  of  the  preparation.  Close  the  key. 
Move  the  slider  along  the  wire. 

When  the  current  taken  off  reaches  the  thres- 
hold value,  the  apex  will  begin  to  beat  rhyth- 
mically. Increasing  the  current  strength  will 
increase  (within  limits)  the  frequency  of  con- 
traction. 

Skeletal  Muscle.  —  The  curarized  sartorius  may 
sometimes  be  brought  into  rhythmic  contrac- 
tion by  constant  currents  (Hering).  If  the 
irritability  of  the  muscle  at  the  point  of  stimula- 
tion be  increased  by  applying  to  the  cathodal 
region  a  two  per  cent  solution  of  sodium  carbon- 
ate, the  constant  current  will  produce  strong 
rhythmic  contractions. 

Smoke  a  drum.  Fasten  the  pelvic  end  of  the 
sartorius  in  the  muscle  clamp,  and  attach  the 
tibial  end  by  a  thread  to  the  vertical  pin  on  the 


STIMULATION    OF   MUSCLE   AND   NERVE        105 

muscle  lever  so  that  the  horizontally  extended 
muscle  may  write  its  contraction  on  a  drum. 
Lay  on  the  tibial  fifth  of  the  muscle  a  piece  of 
filter  paper,  wet  with  two  per  cent  solution  of 
sodium  carbonate.  Connect  a  dry  cell  through 
a  simple  key  with  the  metre  posts  of  the  rheo- 
cord.  Connect  the  non-polarizable  electrodes  with 
the  positive  post  and  the  slider.  Bring  the  slider 
near  the  positive  post.  When  the  sodium  car- 
bonate has  acted  for  15  minutes,  bring  the 
cathode  against  the  tibial  end,  the  anode  against 
the  pelvic  end  of  the  muscle.  Close  and  open  the 
circuit,  moving  the  slider  meanwhile  to  find 
the  current  which  will  give  closing  contraction. 
At  this  point  keep  the  circuit  closed. 

Rhythmical  contractions  usually  appear. 

Periodic  contractions  are  observed  also  in 
smooth  muscle,  stimulated  with  the  constant 
current.  Any  form  of  constant  stimulus  will 
serve  to  produce  them,  pressure  —  as  in  the 
heart,  bladder,  and  intestine  —  and  chemical 
action,  being  especially  noteworthy. 

Continuous  Galvanic  Stimulation  of  Nerve  may- 
cause  the  Periodic  Discharge  of  Nerve  Impulses.  — 
If  two  non-polarizable  electrodes  are  allowed  to 
rest  on  the  muscle  (horizontally  suspended),  and 
are  connected  to  a  capillary  electrometer,  the 
meniscus  of  which   is   projected  through  a  slit 


106      THE   PHYSIOLOGY   OF   MUSCLE   AND    NERVE 

onto  rapidly  moving  sensitized  paper,  the  shadow 
of  the  meniscus  will  make  a  straight  line  on  the 
photographic  paper  so  long  as  the  muscle  is  at 
rest.  When,  however,  the  nerve  of  the  muscle 
is  stimulated  with  the  galvanic  current  and 
closing  tetanus  appears,  the  straight  line  will  be 
broken  by  10-15  oscillations  per  second.  These 
oscillations  are  produced  by  the  difference  of  poten- 
tial created  by  each  contraction  wave  as  it  passes 
over  the  muscle  (contracting  muscle  is  negative 
towards  muscle  at  rest,  see  page  166),  and  demon- 
strate that  the  tetanus  is  a  fusion  of  individual 
contractions  produced  by  successive  stimuli. 

Hence,  nerve,  like  muscle,  responds  to  a  continu- 
ous stimulus  by  a  periodic  discharge  of  energy. 

Ulnar  Nerve.  —  Connect  15  dry  cells  in  series 
(zinc  to  carbon),  and  join  the  last  zinc  and  carbon 
through  a  key  to  a  small  brass  stimulating  elec- 
trode one  cm.  in  diameter,  and  a  large  "  indiffer- 
ent"  electrode  (brass  plate  6.5  x  3.5  cm.  covered 
with  cotton  wet  in  solution  of  common  salt). 
Hold  the  indifferent  electrode  in  the  left  hand, 
and  apply  the  stimulating  electrode  to  the  ulnar 
nerve  at  the  elbow. 

A  pecular  tingling  sensation  will  be  felt  so 
long  as  the  current  flows. 

Polarization  Current.  —  Let  the  sciatic  nerve 
rest   on  a   pair    of  non-polarizable  electrodes  in 


STIMULATION    OF   MUSCLE   AND    NERVE        107 

the  moist  chamber.     Connect  the   electrodes  to 
the  side  cups  of  the  pole-changer  (without  cross- 
wires).     Connect  one  end  pair  of  the  pole-changer 
cups    with    a   dry   cell. 
Turn  the  rocker  to  the     ^-v^--  /-^""n    _<^~\J 

(o VTrn —  \      ;l 

opposite  side,  to  prevent     v-"/    " ~\zb>    : —   \ 
the  battery  current  from  \    / 

reaching  the  electrodes  ====JLjL= 

until  it  is  wanted.    Con-  Fig.  29. 

nect  the  remaining  pair 

of  cups  through  a  closed  short-circuiting  key  with 
the  capillary  electrometer.  Let  the  galvanic 
current  flow  some  minutes  through  the  nerve, 
then  turn  the  rocker  towards  the  electrometer  and 
open  the  short-circuiting  key. 

Note  a  movement  of  the  meniscus  in  a  direction 
indicating  that  the  former  cathode  is  nowr  posi- 
tive to  the  former  anode.     The  nerve  is  polarized. 

Positive  Variation.  —  If  the  polarizing  current 
is  strong  and  brief,  the  negative  polarization  after- 
current will  speedily  give  place  to  a  positive 
current,  i.  e.  one  in  the  direction  of  the  polarizing 
current.  This  positive  current  is  really  an  action 
current.  When  the  polarizing  current  is  broken, 
the  rise  of  irritability  at  the  anode  stimulates 
points  nearer  the  anode  more  strongly  than  points 
farther  away.  Points  nearer  the  anode  become, 
therefore,  negative  to  points  farther  away,  and 


108   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

a  current  flows  through  the  electrometer  circuit 
from  the  less  negative  to  the  more  negative  pole, 
and  through  the  nerve  in  the  direction  from  anode 
to  cathode.  This  positive  variation  is  seen  only 
in  living  nerves. 

Polar  Fatigue.  —  Connect  non-polarizable  elec- 
trodes through  a  simple  key  with  a  dry  cell. 
Arrange  an  inductorium  for  single  induction 
currents  (the  pole-changer  may  be  placed  in  the 
primary  circuit  as  a  simple  key).  Fatigue  a  sar- 
torius  muscle  by  opening  and  closing  the  gal- 
vanic circuit  (leave  a  brief  interval  between 
opening  and  closure).  Closure  will  at  length  be 
followed  by  no  contraction.  Test  now  the  irrita- 
bility of  the  muscle  by  stimulating  it  with  induc- 
tion currents. 

The  muscle  will  be  irritable  except  in  the  cath- 
odal region.     The  fatigue  has  been  local  (polar). 

Opening  and  Closing  Tetanus  —  1.  Arrange  a 
moist  chamber  with  a  muscle  lever  to  write  on  a 
smoked  drum.  Place  two  non-polarizable  elec- 
trodes in  the  moist  chamber  and  connect  them 
through  a  pole-changer  with  a  dry  cell.  Make  a 
nerve-muscle  preparation  from  a  frog  that  has 
just  been  brought  from  a  cold  room  into  the  warm 
laboratory.  Secure  the  femur  in  the  femur  clamp 
of  the  moist  chamber.  Let  the  nerve  rest  on  the 
non-polarizable  electrodes.      Attach  the   muscle 


STIMULATION    OF    MUSCLE    AND    NERVE        109 

to  the  lever.  Bring  the  writing  point  against  the 
slowly  moving  drum.     Close  the  key. 

If  the  frog  has  been  well  cooled  (below  10°  C), 
the  muscle  will  fall  into  tetanus  both  on  closing 
and  on  opening  the  circuit.  Note  that  the  curve 
is  quite  regular.  If  tetanus  fails  to  appear,  paint 
the  cathodal  region  with  one  per  cent  solution  of 
sodic  carbonate,  thus  raising  the  irritability,  and 
repeat  the  experiment.  The  curve  secured  in 
this  way  is  likely  to  be  irregular. 

Produce  opening  tetanus,  and  while  the  muscle 
is  contracting  close  the  current  again. 

The  tetanus  will  disappear;  the  irritability 
will  be  reduced  in  the  anodal  region,  from  the 
polarization  of  which  the  tetanus  was  produced. 

Open  the  current  again.  When  the  tetanus 
reappears  reverse  the  pole-changer  and  close  the 
current. 

The  tetanus  will  be  increased ;  the  irritability 
in  the  former  anodal  region  will  surfer  a  catelec- 
trotonic  increase. 

2.  A  beautiful  demonstration  of  polar  excitation 
may  be  made  in  this  experiment.  Connect  the 
electrodes  in  such  a  way  that  the  intrapolar  cur- 
rent shall  be  descending  (i.  e.  towards  the  muscle). 
When  the  opening  tetanus  appears,  cut  away 
the  anode  by  severing  the  nerve  between  the 
electrodes. 


110      THE    PHYSIOLOGY    OF   MUSCLE   AND   NERVE 

The  contraction  ceases  with  the  removal  of  the 
source  of  stimulation. 

3.  The  stimulating  effect  of  the  salts  of  the 
alkalies  has  been  explained  by  their  attraction 
for  water,  the  loss  of  which  increases  the  effect 
of  the  galvanic  current  on  nerve.  When  the 
irritability  of  the  nerve  is  raised  by  drying,  weak 
currents  may  give  opening  contractions,  although 
they  are  absent  in  normal,  uninjured  nerves. 
The  interval  between  the  opening  of  the  current 
and  the  resulting  contraction  is  then  markedly 
long.  In  nerves. in  the  first  stage  of  drying  the 
intensity  of  the  nerve  impulse  (height  of  con- 
traction of  attached  muscle)  is  also  more  than 
usually  dependent  on  the  duration  of  the  current. 

4.  The  opening  tetanus  (so-called  Eitter's 
tetanus)  is  probably  caused  by  the  rise  of  irrita- 
bility, which  takes  place  in  the  anodal  region 
when  the  current  is  shut  off,  acting  on  a  nerve 
already  in  latent  excitation.  A  similar  condition 
can  be  produced  as  follows :  — 

Smoke  a  drum.  Connect  a  dry  cell  through  an 
open  key  and  an  electromagnetic  signal  with  the 
metre  posts  of  the  rheocord  (Fig.  30).  Connect 
the  zero  post  and  the  slider  of  the  rheocord 
with  the  pole-changer  (with  cross-wires),  and  the 
latter  with  two  non-polarizable  electrodes  placed 
in  the  moist    chamber.      Make  a  nerve-muscle 


STIMULATION   OF  MUSCLE    A X J >    CTEBVE       111 

preparation,  and  secure  the  femur  in  the  femur 
clamp  of  the  moist  chamber.  Attach  the  muscle 
to  the  muscle  lever.  Bring  the  writing  points 
of  the  muscle  lever  and  the  electromagnetic  sig- 
nal against  the  smoked  surface  in  the  same 
vertical  line.  Let  the  nerve  rest  on  the  non- 
polarizable  electrodes.  In  the  remaining  two 
posts  in  the  moist  chamber  fasten  stimulating 
electrodes.      Connect   the   latter   to   the    induc- 


Fig.  30. 

torium,  arranged  for  tetanizing  currents,  short- 
circuiting  key  closed.  Bring  the  stimulating 
electrodes  against  the  nerve  between  the  non- 
polarizable  electrodes  and  the  muscle.  Let  the 
secondary  coil  be  at  such  a  distance  that  the 
tetanizing  current  will  be  just  below  the  thres- 
hold value.  Turn  the  pole-changer  so  that  the 
anode  shall  be  next  the  tetanizing  electrodes. 
Make  and  break  the  galvanic  current,  recording 
the  contraction  on  a  slowly  moving  drum.     Now 


112      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

open  the  short-circuiting  key,  and  after  half  a 
minute,  and  while  the  sub-minimal  tetanizing 
current  is  still  passing  through  the  nerve,  make 
and  break  the  galvanic  current  again. 

A  moderately  strong  galvanic  current  will  now 
produce  an  opening  tetanus  (anodal  stimulation 
of  a  region  the  irritability  of  which  has  been 
raised  by  the  sub-minimal  tetanizing  current). 
Other  effects  are  a  lengthening  of  the  latent 
period,  and  an  increased  dependence  on  the 
duration  of  the  galvanic  current  (see  page  100). 

Reverse  the  pole-changer,  so  that  the  tetanizing 
electrodes  fall  in  the  cathodal  region.  Repeat 
the  experiment,  comparing  the  results  of  cathodal 
stimulation  without  and  with  the  sub-minimal 
tetanizing  current. 

With  sub-minimal  tetanization,  an  increase  in 
the  height  of  the  closing  contraction,  when  the 
galvanic  current  is  not  too  strong,  will  be  seen ; 
when  the  galvanic  current  is  stronger,  closing 
tetanus  will  also  be  observed. 

Polar  Excitation  in  Injured  Muscle.  —  Smoke  a 
drum.  Make  non-polarizable  electrodes.  Con- 
nect a  dry  cell  through  a  simple  key  and  pole- 
changer  (with  cross-wires)  with  the  non-polariz- 
able electrodes.  Prepare  a  sartorius  muscle  with 
bony  attachments.  Fasten  the  pelvic  end  in 
the  muscle  clamp.     Tie  a  thread  to  the  tibial 


STIMULATION"   OF   MUSCLE   AND   NSKVE      113 

end,  and  fasten  the  thread  to  the  upright  pin  of 
the  muscle  lever,  so  that  the  muscle  is  extended 
horizontally.  Bring  the  writing  point  against  the 
drum.  Light  a  Bunsen  burner.  Heat  a  wire, 
and  kill  the  pelvic  end  of  the  muscle  by  laying 
the  hot  wire  against  it.  Bring  one  non-polariz- 
able  electrode  upon  each  end  of  the  muscle. 
Arrange  the  pole-changer  so  that  the  cathode 
shall  be  at  the  pelvic  end,  and  the  current  there- 
fore "  atterminal,"  i.  e.  directed  toward  the 
"  thermal  cross-section."     Close  the  simple  key. 

No  contraction,  or  a  very  slight  contraction, 
will  be  seen. 

Open  the  key.  Reverse  the  pole-changer,  so 
that  the  current  shall  be  "  abterminal."  Close 
the  simple  key. 

The  ordinary  closing  contraction  will  be  seen. 

The  great  difference  here  shown  between  the 
polar  excitability  in  the  uninjured  and  injured 
region  is  probably  due  to  chemical  changes  in 
the  injured  part.  Similar  results  can  be  obtained 
by  painting  the  end  of  the  muscle  with  one  per 
solution  of  acid  potassium  phosphate.  The 
irritability  is  lessened  by  this  salt  but  returns  to 
normal  if  the  altered  end  of  the  muscle  is  bathed 
in  0.6  per  cent  sodium  chloride  solution. 

Sodium  carbonate  has  an  effect  opposite  to  the 
potassium  salts. 

8 


114      THE    PHYSIOLOGY   OF   MUSCLE   AND    NERVE 

Wet  the  tibial  end  of  the  muscle  with  one 
per  cent  solution  of  sodic  carbonate.  After  a 
short  time,  test  the  irritability  to  weak,  ascend- 
ing (i.  e.  cathode  at  pelvic  end)  currents. 

The  closure  of  ascending  currents  will  give 
extraordinarily  large  contractions. 

The  cause  of  this  change  in  irritability  is  not 
the  presence  of  dead  contractile  tissue,  for  elec- 
trodes can  be  wrapped  in  dead  muscle  and  used 
to  stimulate  normal  muscle  without  loss  of  irri- 
tability being  noticeable. 

When  the  end  of  the  fibre  is  killed,  the  patho- 
logical change  passes  gradually  through  the 
whole  of  the  fibre. 

Polar  Inhibition  by  the   Galvanic  Current 

It  remains  now  to  consider  the  inhibitory 
action  of  the  galvanic  current,  to  which  attention 
was  called  on  page  103. 

Heart.  —  Connect  a  dry  cell  through  a  simple 
key  and  pole-changer  (cross-wires)  with  the  0 
and  1  metre  posts  of  the  rheocord.  Connect 
non-polarizable  electrodes  with  the  slider  and  the 
positive  post  of  the  rheocord.  Place  the  brain- 
less frog,  back  down,  in  the  holder  (Fig.  31)  and 
expose  the  heart,  according  to  the  method  de- 
scribed on  page  75.  Open  the  delicate  membrane 
(pericardium)  which  surrounds  the  heart.     Let 


STIMULATION    OF   MUSCLE   AND    NERVE        115 

one  electrode  rest  on  the  larynx.  Fasten  the 
other  in  the  muscle  clamp,  and  bring  it  over 
the  heart  so  that  the  tip  of  the  brush  rests  on 
the  ventricle  and  moves  with  it.  Turn  the  pole- 
changer  to  make  this  electrode  the  anode.  Make 
the  current. 

At  each  systole,  the  portion  of  the  ventricle 
immediately  about  the  anode  will  not  contract 
with  the  rest,  but  will  remain  relaxed  (local  dias- 
tole). Thus  while  the  greater  part  of  the  ven- 
tricle becomes  pale  as  the  blood  is  squeezed  out 
of  its  wall  by  the  con- 
traction, the  anodal  re- 
gion remains  dark  red. 
From   this  region  the  Fis" 8L  Tbe  fr°e-board- 

relaxation  spreads  over  the  rest  of  the  ventricle. 
Keverse  the  pole-changer.     Break  the  current. 

The  cardiac  electrode  is  now  the  cathode.  In 
the  systole  following  the  breaking  of  the  current, 
the  cathodal  region  will  remain  relaxed  during 
contraction  of  the  ventricle. 

This  experiment  demonstrates  that  the  galvanic 
current  not  only  may  stimulate,  but  may  check 
or  inhibit  contraction.  In  the  former  case,  the 
conversion  of  potential  into  active  energy  is  set 
going ;  in  the  latter,  it  is  prevented.  Inhibi- 
tion plays  a  large  part  in  the  physiology  of  the 
day. 


116      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

Polar    Inhibition   in    Veratrinized   Muscle.  —  A 

similar  inhibitory  effect  can  be  demonstrated  in 
skeletal  muscle  previously  placed  in  continued 
("tonic")  contraction  by  veratrine  poisoning. 
Inject  with  a  fine  glass  pipette  seven  drops  of 
one  per  cent  solution  of  veratrine  acetate  in  the 
dorsal  lymph  sac  of  a  frog. 

Arrange  two  muscle  levers  to  write  on  a  drum. 
Between  them  place  an  electromagnetic  signal. 
Let  all  three  writing  points  be  in  the  same  vertical 
line.  Connect  a  dry  cell  through  a  simple  key 
with  an  inductorium  arranged  for  single  induc- 
tion shocks.  Connect  non-polarizable  electrodes 
through  ■  another  simple  key  and  the  electro- 
magnetic signal  with  a  dry  cell.  Prepare  a 
sartorius  muscle  with  pelvic  and  tibial  attach- 
ments. Fasten  the  muscle  about  the  middle  in 
the  cork  clamp.  Fasten  the  cork  clamp  verti- 
cally in  the  jaws  of  the  muscle  clamp.  Carry 
threads  from  each  end  of  the  muscle  to  one  of 
the  muscle  levers.  Place  the  non-polarizable 
electrodes  near  the  respective  ends  of  the  mus- 
cle. Note  which  is  the  anode.  Bring  wires 
from  the  secondary  coil  of  the  inductorium  to 
the  ends  of  the  muscle.  Start  the  drum  mov- 
ing slowly.  Stimulate  the  muscle  with  a  single 
induction  shock.  There  will  be  a  prolonged  con- 
traction, characteristic  of  veratrine  poisoning.    So 


STIMULATION   OF   MUSCLE   AND   NERVE       117 

soon  as  this  contraction  is  well  under  way,  make 
the  constant  current. 

The  anodal  half  of  the  muscle  will  show  a  dis- 
tinct relaxation  ;  the  cathodal  half  will  not  relax, 
but  may  even  contract  a  little  more. 

Stimulation  affected  by  the  Form  of  the 
Muscle 

Connect  a  dry  cell  through  a  simple  key  to 
the  metre  posts  of  the  rheocord.  Bring  wires 
from  the  non-polarizable  electrodes  to  the  positive 
post  and  the  slider,  interposing  the  pole-changer 
with  cross-wires  so  that  the  direction  of  the  cur- 
rent can  he  changed.  Place  the  slider  against 
the  positive  post,  so  that  all  the  current  passes 
back  to  the  cell. 

Prepare  a  curarized  sartorius  muscle  with  its 
bony  attachments.  Fasten  the  pelvic  fragment 
in  the  muscle  clamp.  Tie  a  thread  about  the 
tibia  and  fasten  the  thread  to  the  upright  pin  of 
the  muscle  lever.  Let  the  cathode  rest  on  the 
tibial  end  of  the  muscle,  the  anode  on  the  pelvic 
end  ;  the  current  will  then  be  descending.  Move 
the  slider  a  few  centimetres  away  from  the  posi- 
tive post,  and  make  the  current.  If  no  contrac- 
tion follows,  move  the  slider  farther  along,  and 
make  the  current  again. 

With  careful  work,  it  will  be  shown  that  with 


118      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

descending  currents,  the  first  contraction  will 
be  on  closure  only.  With  ascending  currents, 
the  first  contraction  will  be  on  opening  the 
current. 

The  explanation  is  that,  with  currents  which 
pass  through  the  sartorius  from  end  to  end 
the  point  of  greatest  density  is  the  smaller, 
lower  end.  This  is  cathodal  in  descending 
currents,  anodal  in  ascending  currents. 

Effect  of  the  Angle  at  which  the  Current 
Lines  cut  the  Muscle  Fibres 

Connect  non-polarizable  electrodes  through 
a  key  with  a  dry  cell.  Build  on  a  glass  plate 
with  normal  saline  clay  two  parallel  walls  a 
little  longer  than  the  sartorius  muscle  and 
one  centimetre  apart.  Join  the  ends  with 
clay,  to  make  a  rectangular  trough.  Eemove 
a  sartorius  muscle  from  a  curarized  frog, 
avoiding  all  injury  to  the  muscle.  Place  the 
muscle  in  the  trough,  and  cover  it  with  normal 
saline  solution.  Bring  a  non-polarizable  elec- 
trode against  the  centre  of  each  long  side,  so 
that  the  current  lines  shall  cut  the  muscle 
fibres  at  right   angles.     Close  the  key. 

There  will  be  no  contraction.  The  muscle  is 
inexcitable  to  currents  that  cross  its  fibres  at 
right  angles. 


STIMULATION    OF   MUSCLE   AND    NERVE        119 

Alter  the  angle  by  moving  one  electrode  to 
the  right,  the  other  to  the  left,  and  repeat  the 
experiment. 

The  stimulating  effect  will  increase  as  the 
angle  between  current  lines  and  the  long  axis  of 
muscular  fibres  diminishes. 

Nerves  also  are  inexcitable  to  transverse  cur- 
rents. Differences  in  resistance  play  a  great 
part  here.  The  resistance  of  nerves  is  said  to 
be  2.]-  million  times  that  of  mercury,  when  the 
current  passes  along  the  nerve,  and  12|  million 
times  when  it  passes  transversely. 

The  Induced  Current 

The  break  induction  current,  owing  to  its  rapid 
rise  from  zero  to  maximum  intensity,  is  a  more 
effective  physiological  stimulus  than  the  make 
current,  and  may  therefore  be  chosen  for 
experimentation. 

1.  The  direction  of  the  induction  current  in 
the  secondary  coil  is  most  easily  determined 
electrolytically. 

Arrange  the  inductorium  for  maximal  currents. 
Bring  wires  from  the  posts  on  the  secondary  coil 
to  a  piece  of  filter  paper  wet  with  starch  paste 
containing  iodide  of  potassium.  Exclude  the 
make   currents   with   the    short-circuiting    key  ; 


120   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

pass  the  maximal  break  currents  through  the 
electrolyte. 

Iodine  will  be  set  free  at  the  anode  and  will 
combine  with  the  starch  to  form  blue  iodide  of 
starch. 

Mark  the  positive  post  on  the  secondary  coil 
with  a  plus  sign. 

2.  Connect  the  poles  of  the  secondary  coil 
through  a  pole-changer  with  non-polarizable 
electrodes.  Make  a  nerve-muscle  preparation. 
Tie  a  ligature  about  the  nerve  about  two  cen- 
timetres from  the  central  end.  Place  one  elec- 
trode on  each  side  of  the  ligature.  The  passage 
of  a  nerve  impulse  from  the  central  electrode 
to  the  muscle  will  be  prevented  by  the  lig- 
ature, although  the  electric  current  can  still 
pass  between  the  electrodes.  Turn  the  pole- 
changer  so  that  the  electrode  on  the  periph- 
eral (muscle)  side  of  the  ligature  shall  be  first 
the  anode  and  then  the  cathode,  and  test  the 
irritability  to  weak  induction  currents,  begin- 
ning with  the  secondary  coil  some  distance  from 
the  primary,  and  gradually  increasing  the  intensity. 

Only  cathodal  stimulation  will  produce  con- 
traction. The  same  result  can  be  secured  by 
separating  the  cathode  and  anode  with  ammonia. 
If  the  nerve  is  painted  with  ammonia  in  the 
intrapolar  region,  break  currents  cease  to  cause 


STIMULATION   OF   MUSCLE   AND   NERVE       121 

contraction  when  the  cathode  is  on  the  central 
side  of  the  painted  zone.  Painting  the  cathodal 
region  directly  also  prevents  excitation. 

The  failure  of  the  induction  current  to  stimu- 
late at  the  anode,  on  opening  the  current,  is  due 
to  the  exceedingly  brief  duration  of  the  induced 
current ;  there  is  not  time  for  a  sufficient  anelec- 
trotonic  alteration  in  excitability.  If  the  current 
is  shortened  still  more  (if  it  be  less  than  0.0015 
sec),  the  cathodal  excitation  also  disappears. 
With  very  strong  currents,  however,  opening  the 
current  stimulates  as  well  as  closure. 

3.  Additional  evidence  of  polar  action  is 
secured  by  connecting  the  electrodes  with  the 
capillary  electrometer  through  a  closed  short- 
circuiting  key.  The  meniscus  is  brought  into 
the  field,  the  nerve  is  stimulated  repeatedly 
with  maximal  break  currents,  and  then  stimu- 
lation is  stopped,  and  the  short-circuiting  key 
in  the  electrometer  circuit  opened.  The  menis- 
cus will  move  in  a  direction  indicating  a  higher 
potential  at  the  anode  (positive  anodal  polariza- 
tion current). 

4.  Finally,  it  may  be  added  that  the  galvanic 
current  may  increase  the  stimulating  effect  of  the 
induced  current  as  pointed  out  on  page  80,  but  i  inly 
when  the  cathode  of  the  induced  current  falls  in 
the  cathodal  region  of  the  polarizing  current. 


122   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

The  law  of  polar  excitation  holds  good  then 
for  the  induced  as  well  as  the  galvanic  current. 
In  fact,  there  is  no  essential  difference  between 
the  physiological  effects  of  induced  currents  and 
very  brief  galvanic  currents. 

Increasing  the  intensity  of  the  induced  cur- 
rent increases  at  first  the  excitation  (height  of 
contraction).  At  length,  however,  with  ascend- 
ing currents,  a  point  is  reached  beyond  which 
further  increase  in  strength  is  followed  first  by 
the  diminution  and  at  length  by  the  disappear 
ance  of  contraction.  With  still  higher  intensi- 
ties, the  contractions  reappear.  This  gaf  in  the 
contraction  series  is  explained  by  the  increasing 
depression  of  irritability  at  the  anode  blocking 
the  cathodal  impulse ;  when  the  intensity  is  still 
further  increased,  the  opening  of  the  current  acts 
as  a  stimulus.  A  similar  result  may  be  secured 
with  the  galvanic  current. 

Apparatus 

Normal  saline.  Bowl.  Pipette.  Towel.  Simple  key. 
Non-polarizable  electrodes.  Nerve  holder.  Potter's  clay 
mixed  with  0.6  per  cent  solution  of  sodium  chloride. 
Saturated  solution  of  zinc  sulphate.  Muscle  clamp. 
Stand.  13  wires.  Kymograph.  Glazed  paper.  Two 
muscle  levers.  Thread.  Eheocord.  Two  dry  cells. 
Moist  chamber.  Glass  plate.  Ice.  Paraffin  paper.  Cork 
clamp.    Pole-changer.    Beaker.    Tripod.    Sodium  chloride. 


STIMULATION   OF  MUSCLE   AND   NERVE        123 

Inductorium.  Electrodes.  Bunsen  burner.  Intestine  of 
a  rabbit.  Electromagnetic  signal.  Tuning  fork.  Brass 
electrodes.  Fine  copper  wire.  Frog  board.  2  pairs  of 
metal  electrodes,  each  passed  through  cork.  Electrom- 
eter. Paramecia.  Microscope.  Glass  slide.  Bent  hooks. 
One  per  cent  solution  of  veratrine  acetate.  Fine  glass 
pipette.  Filter  paper  saturated  with  starch  paste  con- 
taining potassium  iodide.  Frogs.  Fine  rubber  tubing 
for  insulating  electrodes.  Ammonia.  One  per  cent  solu- 
tion of  acid  potassium  phosphate.  Two  per  cent  solution 
of  sodic  carbonate.     Ligatures.     Filter  paper. 


124      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 


CHEMICAL  AND   MECHANICAL  STIMULATION 

Chemical  Stimulation 

The  contractility,  heat  production,  and  other 
phenomena  of  the  life  of  muscle  rest  at  base  on 
chemical  processes.  Anything  that  sufficiently 
alters  these  processes  may  be  a  stimulus.  A  most 
important  source  of  stimulation  is  the  alteration 
of  the  chemical  composition  of  muscle  through 
osmosis. 

Effect  of  Distilled  Water.  —  Place  a  sartorius 
muscle  in  distilled  water. 

Irregular  contractions  usually  occur.  The 
muscle  soon  swells,  and  becomes  white,  turbid, 
cadaveric. 

These  striking  changes  depend  on  the  with- 
drawal of  certain  bodies  by  osmosis.  Muscle 
contains  large  quantities  of  proteid,  particularly 
proteids  of  the  globulin  class ;  certain  carbo- 
hydrates, such  as  glycogen ;  nitrogenous  and 
other  extractives  ;  water ;  and  a  number  of  in- 
organic salts.  Most  of  these  bodies  are  largely 
or  wholly  insoluble  in  water,  and  require  for 
their   solution  the   presence  of   inorganic  salts. 


-CHEMICAL   AND   MECHANICAL   STIMULATION      125 

The  globulins,  for  example,  are  insoluble  in  dis- 
tilled water,  but  soluble  in  dilute  solutions  of 
sodium  chloride.  The  osmosis  of  salts  into  the 
distilled  water  in  the  above  experiment  first 
stimulates  and  then  destroys  the  contractility 
of  the  muscle. 

An  increase  in  the  saline  content  of  the  muscle 
juice  or  "  plasma  "  also  acts  as  a  stimulus,  and,  if 
excessive,  may  be  fatal. 

Strong  Saline  Solutions.  —  Place  a  sartorillS 
muscle  on  a  slightly  inclined  glass  plate.  Cover 
the  lowest  fourth  of  the  muscle  with  crystals  of 
sodium  chloride. 

Irregular  contractions  will  appear. 

Drying.  —  The  effect  of  loss  of  water  is  best 
shown  in  nerve. 

Let  the  nerve  of  a  nerve-muscle  preparation 
dry.  Note  the  twitching  of  the  muscle  as  the 
water  content  diminishes.  Test  the  irritability 
of  the  nerve  from  time  to  time  with  induction 
currents.  It  will  first  increase,  then  disappear 
as  the  nerve  dries. 

Wet  the  nerve  with  0.6  per  cent  sodium 
chloride  solution. 

The  contractions  will  disappear. 

To  keep  muscles  and  nerves  in  good  condition 
for  experimentation,  it  is  necessary  to  moisten 
them  with  a  solution  containing  the  inorganic 
salts  most  abundant  in  the  tissue-liquids  in  the 


126      THE   PHYSIOLOGY    OF   MUSCLE    AND   NEKVE 

proportions  in  which  they  are  present  in  those 
liquids.  Practically,  a  0.6  per  cent  solution  of 
sodium  chloride  has  commonly  been  employed, 
in  the  case  of  the  frog.  Such  a  solution  is  said 
to  be  isotonic,  i.  e.  neither  giving  nor  taking 
water  from  the  tissue.  That  it  is  not  perfectly 
indifferent  appears  from  this  experiment. 

"Normal  Saline."  —  Allow  a  sartorius  muscle 
to  stand  half  an  hour  in  normal  saline  solution 
(0.6  per  cent  NaCl).  Kecord  its  contraction  in 
response  to  a  maximal  break  induction  current. 
In  place  of  a  simple  twitch  a  tetaniform  con- 
traction of  abnormal  height  and  duration  will 
usually  be  secured. 

Importance  of  Calcium.  —  Place  the  "  normal 
saline  "  sartorius  in  0.6  per  cent  sodium  chloride 
solution  containing  10  per  cent  of  saturated  solu- 
tion of  calcium  sulphate.  After  10  minutes 
record  the  maximal  break  contraction. 

The  abnormal  tetaniform  contraction  will  have 
disappeared. 

Constant  Chemical  Stimulation  may  cause  Peri- 
odic Contraction.  —  Place  a  sartorius  muscle  in  a 
solution  of  5  grams  NaCl,  2  grams  ISTa2HP04,  and 
0.4  gram  Na2C03  in  one  litre  of  distilled  water. 

Usually  rhythmic  contractions  are  seen.  All 
contractile  substance  shows  a  tendency  to  peri- 
odic contractions  in  response  to  a  constant  stimu- 


CHEMICAL    AND    MECHANICAL    STIMULATION       127 

lus,  whether  chemical,  mechanical,  or  electrical. 
There  are  reasons  for  believing  that  the  rhythmi- 
cal contractions  of  the  heart  are  the  consequence 
of  a  constant  chemical  stimulus. 

Mechanical  Stimulation 

Stimulate  a  nerve  mechanically  by  pinching 
the  cut  end  with  forceps. 

No  change  will  be  seen  in  the  nerve,  but  the 
muscle  will  shorten,  and  then  relax. 

Mechanical  stimulation  has  the  advantage  that 
it  can  be  localized  accurately,  and  for  this  reason 
it  has  been  used  where  electrical  stimulation 
seemed  inapplicable.  Tetauomotors  have  been 
constructed  by  Heidenhain  and  others  to  give  a 
rapid  succession  of  slight  blows  upon  the  nerve. 

Sudden  pressure  on  a  muscle  or  sudden  exten- 
sion may  cause  contraction.  "  Sometimes  the 
whole  muscle  contracts,  sometimes  only  the 
portion  directly  stimulated. 

Idio-Muscular  Contraction.  —  "With  the  point 
of  the  seeker  stroke  the  diaphragm  and  other 
muscles  of  a  recently  killed  rat,  or  other  small 
warm-blooded  animal,  in  a  direction  at  right 
angles  to  the  course  of  the  fibres. 

A  wheal,  i.  c.  a  long-continued  shortening  and 
thickening  of  the  fibre  stimulated,  will  be  seen. 
If  the  animal  be  not  too  long  dead,  a  momentary 


128      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

twitch,  of  the  whole  of  the  fibre  stimulated  will 
precede  the  continued  local  contraction  or  wheal. 
The  same  phenomenon  is  seen  for  a  briefer 
time  on  sharp  mechanical  stimulation  of  muscles 
in  living  animals,  for  example,  the  wheals  raised 
by  the  blow  of  a  whip.  In  men  long  ill  of  wast- 
ing diseases,  c.  g.  phthisis,  the  idio-muscular  con- 
tractions appear  on  drawing  a  pencil  point  across 
the  muscles.  Direct  total  stimulation  of  frog's 
muscle,  especially  in  the  spring  months,  may  be 
followed  by  long  continued  contraction.  Fatigue, 
cold,  and  many  poisons,  such  as  veratrine,  favor 
the  prolongation  of  the  phase  of  shortening.  The 
idio-muscular  contraction  is  not  a  "  tetanus," 
i,  e.  not  a  prolonged  shortening  due  to  successive 
contractions,  the  interval  between  which  is  too 
short  to  permit  of  relaxation,  but  a  prolonged 
single  contraction,  the  cause  of  which  lies  in  the 
muscle  and  not  in  the  nerve. 

Apparatus 

Normal  saline.  Bowl.  Pipette.  Towel.  Glass  plate. 
Distilled  water.  Sodium  chloride.  Solution  of  sodium 
chloride  (0.6  per  cent),  containing  10  per  cent  of  saturated 
solution  of  calcium  sulphate.  Solution  containing  5  grams 
sodium  chloride,  2  grams  di-sodium  hydrogen  phosphate, 
and  0.4  gram  sodium  carbonate,  in  1000  c.c.  water.  Small 
warm-blooded  animal  recently  killed.  Introduction  coil. 
Dry  cell.     Key.     Electrodes.     3  Wires.     Frogs. 


IRRITABILITY   AND   CONDUCTIVITY  129 


VI 
IRRITABILITY   AND   CONDUCTIVITY 

Irritability  is  the  power  of  discharging  energy 
on  stimulation.  The  form  in  which  the  kinetic 
energy  of  muscle  appears  is  partly  mechanical 
work  (the  visible  contraction)  and  partly  molec- 
ular, —  heat,  chemical  action,  and  electricity. 
In  the  nerve,  the  kinetic  energy  is  wholly  molec- 
ular ;  an  electromotive  force  is  generated,  prob- 
ably heat  is  set  free  (though  this  statement  — 
which  is  based  simply  on  analogy  —  is  frequently 
disputed),  and  a  molecular  change — the  nerve 
impulse  —  arises  at  the  seat  of  stimulation.  In 
both  muscle  and  nerve,  by  virtue  of  their  con- 
ductivity, the  change  induced  by  stimulation  is 
as  a  rule  not  limited  to  the  region  stimulated,  but 
passes  in  both  directions  along  each  stimulated 
fibre.  In  neither  muscle  nor  nerve  can  the 
changes  in  energy  spread  transversely  ;  they  are 
limited  to  the  muscle-  or  nerve-fibre  in  which 
they  arise. 

It  will  be  shown  that  conductivity  and  irrita- 
bility are  essentially  different  functions. 
9 


130      THE    PHYSIOLOGY   OF   MUSCLE   AND    NEEVE 

The   Independent  Irritability  of  Muscle.  —  The 

stimulus  that  causes  the  contraction  of  a  muscle 
may  be  applied  either  to  the  nerve  or  to  the 
muscle  itself.  If  to  the  nerve,  the  muscle  will 
be  thrown  into  the  active  state  not  by  the  origi- 
nal stimulus,  but  by  a  nerve  impulse.  If  to  the 
muscle,  the  nerve  will  still  be  stimulated,  for 
examination  shows  terminal  fibres  distributed,  in 
skeletal  muscle  at  least,  probably  to  every  fibre, 
and  with  few  exceptions  to  all  parts  of  the 
muscle.  The  fact  that  muscles  may  contract 
when  an  electric  current  flows  through  them,  or 
when  otherwise  stimulated,  does  not  therefore  of 
itself  indicate  that  electricity  is  a  stimulus  to 
muscle  protoplasm.  Before  this  can  be  estab- 
lished, it  will  be  necessary  to  demonstrate  con- 
traction in  parts  of  muscle  not  provided  with 
nerves ;  for  example,  the  distal  part  of  the  sar- 
torius,  or  in  muscles  in  which  the  nerves  have 
been  destroyed  by  curare  or  by  degeneration. 

Nerve-free  Muscle.  —  Kemove  the  sartorius 
muscle,  together  with  the  portion  of  the  pelvis 
and  the  tibia  to  which  the  muscle  is  attached, 
and  lay  it  on  a  glass  plate.  Stimulate  the  distal 
(tibial)  fifth,  in  which  examination  with  the 
microscope  would  show  the  absence  of  nerve 
fibres,  with  a  strong  break  induction  current. 

The  nerve-free  muscle  will  contract. 


IRRITABILITY   AND   CONDUCTIVITY  131 

Muscle  with  Nerves  Degenerated.  —  A  nerve 
fibre  severed  from  its  cell  of  origin  dies  or  "  de- 
generates  "  down  to  its  ultimate  endings.  Expose 
the  sciatic  nerve  in  the  middle  of  the  thigh  of  a 
frog  in  which  the  nerve  has  been  severed  near 
the  pelvis  ten  days  before,  so  that  the  whole  of 
the  nerve  distal  to  the  section  shall  have  degen- 
erated.    Stimulate  the  degenerated  trunk. 

No  contraction  is  seen  in  the  muscles  of  the 
leg.     Stimulate  the  muscles  directly. 

Contraction  takes  place. 

The  Nerve-free  Embryo  Heart.  —  Embryological 
studies  show  that  the  nerves  of  the  heart  are 
formed  from  epiblast  in  the  walls  of  the  neural 
canal,  and  do  not  grow  into  the  heart  until  the 
close  of  the  third  day  of  incubation  (chick). 
The  heart,  however,  begins  to  beat  during  the 
second  day  of  embryonic  life,  before  even  the 
blood  which  it  shall  pump  is  formed.  Thus 
the  heart  muscle,  in  the  embryo,  is  capable  of 
contraction  in  the  absence  of  nerves. 

Cover  an  egg  which  has  been  incubated  60-70 
hours  with  0.75  per  cent  solution  of  sodium 
chloride  warmed  to  38°  C.  Kemove  the  shell 
with  the  forceps  over  one  third  of  the  egg,  be- 
ginning at  the  broad  end,  and  leaving  the  shell 
membrane  behind.  Now  remove  the  shell  mem- 
brane.    Note  the  beating  heart. 


132   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

Paralysis  of  Nerve  Endings  with  Curare.  —  De- 
stroy the  brain  with  the  seeker  as  follows,  avoid- 
ing all  unnecessary  injury  :  Wrap  the  frog  in  the 
cloth,  head  out.  Hold  the  frog  with  the  fingers 
of  the  left  hand,  pressing  down  the  tip  of  the 
frog's  nose  with  the  left  thumb.  Pass  the  right 
forefinger  along  the  middle  line  of  the  head.  A 
slight  depression  will  be  felt  at  the  joining  of 
the  skull  and  trunk.  Here  the  cerebro-spinal 
canal  has  no  bony  covering.  Make  at  this  point 
a  cut  about  a  centimetre  (§  inch)  long  through 
the  skin  in  the  middle  line.  Thrust  the  seeker 
vertically  through  the  soft  tissues  until  the  point 
is  stopped  by  the  bony  vertebrae.  Turn  the 
point  of  the  seeker  towards  the  head,  and  push 
it  along  the  brain  cavity,  moving  it  slightly  from 
side  to  side.  Expose  the  sciatic  nerve  in  the 
thigh  of  one  side,  e.  g.  the  left,  making  a  small 
slit  through  the  skin  in  the  upper  part  of  the 
thigh  over  the  course  of  the  nerve,  and  taking 
the  greatest  care  not  to  injure  the  femoral  artery 
and  vein.  Pass  a  stout  ligature  beneath  the 
nerve  and  around  the  thigh,  as  near  the  trunk 
as  possible,  and  tie  it  firmly  with  a  square  knot. 
A  piece  of  filter  paper,  wet  with  normal  saline 
solution,  should  be  kept  on  the  nerve  where  it 
crosses  the  ligature.  The  left  hind  limb  below 
the  ligature  is  thus   excluded  from  the  circula- 


IRRITABILITY   AND   CONDUCTIVITY  133 

tion.  With  a  fine  glass  pipette  inject  a  few- 
drops  of  a  one  percent  solution  of  curare  through 
a  very  small  hole  made  in  the  skin  of  the  hack 
into  the  dorsal  lymph  sac.  Test  the  reflexes  at 
intervals  of  a  few  minutes  by  stimulating  the 
skin  of  the  feet  with  tetanizing  currents. 

At  an  early  stage  in  the  action  of  the  poison, 
the  right  leg  will  no  longer  be  drawn  up  when 
the  feet*  are  stimulated,  although  the  left  leg, 
from  which  the  poison  is  excluded  by  the  ligation 
of  the  blood-vessels,  still  responds  by  reflex  con- 
tractions, not  only  to  stimulation  of  its  own  foot, 
but  also  to  strong  stimulation  of  the  other  leg. 
The  afferent  (sensory)  nerves,  the  spinal  reflex 
mechanisms,  and  that  part  of  the  efferent  nerves 
which  lies  above  the  level  of  the  ligature  are] 
therefore,  still  functional.  The  reflex  power  is 
lost  on  the  right  side,  because  either  the  trunk  of 
the  nerve,  its  end-organ,  or  the  muscle,  has  been 
paralyzed 

When  all  reflexes  have  ceased,  except  in  the 
ligatured  limb,  lay  bare  the  sciatic  nerves  from 
the  vertebral  column  to  the  knee.  Stimulate 
the  right  nerve  with  the  interrupted  induction 
current. 

There  will  be  no  contraction. 

Stimulate  the  left  nerve  above  the  ligature,  i.  e. 
in  the  region  supplied  with  poisoned  blood. 


134   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

Contraction  follows.  The  trunk  of  this  (left) 
nerve  is  still  functional,  although  supplied  with 
the  poisoned  blood.  Consequently  the  failure 
to  obtain  contraction  on  stimulating  the  right 
nerve  cannot  be  due  to  the  poisoning  of  the 
trunk  of  that  nerve.  The  curare  must  then 
have  paralyzed  either  the  muscle  or  the  endings 
of  the  nerve  in  the  muscle. 

Stimulate  the  right  gastrocnemius  muscle. 

It  contracts.  This  muscle  was  supplied  with 
curare  blood. 

The  curare  has  therefore  paralyzed  the  end- 
organ  of  the  motor  nerve,  probably  the  end- 
plates,  the  muscle  and  the  nerve-trunk  remaining 
functional.  It  follows  that  muscles  can  be  made 
to  contract  without  the  agency  of  nerves.  The 
occurrence  of  idio-muscular  contraction  (see 
page  127)  is  an  additional  proof  of  the  inde- 
pendent irritability  of  muscle. 

Irritability  and  Conductivity  are  Separate  Prop- 
erties of  Nerve.  —  1.  Carbon-dioxide.  —  Arrange 
the  inductorium  for  tetanizing  currents.  Connect 
the  secondary  coil  with  the  main  posts  of  the 
pole-changer  (cross-wires  out).  Connect  the 
two  other  pairs  of  posts  with  the  usual  stimula- 
tion electrodes  and  the  electrodes  of  the  small 
gas  chamber  (Fig.  32).  Join  the  inflow  tube  of 
the  gas  chamber  with  the  outflow  tube  of  the 


IRRITABILITY   AND   CONDUCTIVITY 


13i 


carbon-dioxide  bottle.  The  gas  chamber  should 
rest  on  a  glass  plate.  Make  a  nerve-muscle 
preparation,  preserving  the  full  length  of  the 
sciatic  nerve  up  to  the  vertebral  column.  Tie 
a  silk  thread  to  the  extreme  end  of  the  nerve, 
and  fasten  the  thread  to  the  end  of  the  seeker 
by  a  drop  of  wax  cement.  With  the  aid  of  the 
seeker,  pass  the  thread  through  the  holes,  and 


Fig.  32.  The  gas  chamber,  with  bottle  for  generating  carbon  dioxide, 
ami  a  pole-changer  arranged  to  stimulate  the  nerve  either  within  or  without 
the  chamber.  The  holes  in  the  glass  through  which  the  nerve  passes  are 
plugged  with  normal  saline  clay. 

draw  the  nerve  after,  so  that  the  nerve  lies  on 
the  electrodes.  The  nerve  should  be  drawn 
through  until  the  muscle  is  close  to  the  gas 
chamber.  Stop  up  the  holes  through  which  the 
nerve  passes  with  normal  saline  clay.  Bring  the 
outer  pair  of  electrodes  against  the  central  end 
of  the  nerve  near  its  exit  from  the  gas  chamber. 
Determine   which   position   of   the  pole-changer 


136   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

corresponds  to  each  pair  of  electrodes.  Stimulate 
the  nerve  first  within  the  chamber,  and  then  on 
the  central  side  of  the  chamber,  using  a  current 
just  sufficient  to  cause  tetanus.  In  both  cases 
tetanus  will  result.  Now  pour  20  per  cent 
hydrochloric  acid  onto  the  marble  in  the  gen- 
erator. After  the  gas  has  passed  through  the 
chamber  for  some  time,  stimulate  as  before. 

Stimulation  of  the  portion  of  the  nerve  exposed 
to  the  carbon-dioxide  is  no  longer  effective,  while 
stimulation  of  the  part  central  to  the  gas  chamber 
still  produces  tetanus. 

But  the  nerve  impulses  created  by  stimulation 
of  the  nerve  central  to  the  gas  chamber  cannot 
reach  the  muscle  except  by  passing  along  the 
nerve  and  through  the  carbon-dioxide.  The  con- 
ductivity of  the  nerve  therefore  is  still  sufficient, 
while  the  irritability  has  been  suspended  by  the 
action  of  the  gas.  Hence,  conductivity  and  irri- 
tability are  by  no  means  interchangeable  terms. 

Their  essential  difference  is  further  shown  by 
the  effect  of  alcohol  vapor,  which  impairs  con- 
ductivity while  irritability  is  little  changed. 

2.  Alcohol.  —  Disconnect  the  rubber  tube  from 
the  gas  generator,  and  blow  through  the  gas 
chamber  until  the  carbon-dioxide  is  driven  out. 
The  nerve  will  recover  its  irritability.  Deter- 
mine  this   by   stimulating   from   time  to  time. 


IRRITABILITY  AND   CONDUCTIVITY  137 

When  the  nerve  has  recovered,  drop  a  little 
alcohol  through  the  long  glass  tuhe  of  the  gas 
chamber,  being  careful  that  only  the  vapor  of 
the  alcohol  comes  into  contact  with  the  nerve. 
Stimulate  both  within  and  central  to  the  chamber. 

After  a  time,  tetanus  will  no  longer  be  pro- 
duced by  stimulating  central  to  the  chamber. 
Stimulation  within  the  latter  is  still  effective. 
Thus  conductivity  is  impaired,  while  irritability 
remains  intact,  or  at  least  is  affected  to  a  less 
extent.  (The  electrodes  within  the  alcohol  at- 
mosphere should  not  be  too  far  from  the  opening 
through  which  the  nerve  passes  to  the  muscle, 
else  the  loss  of  conductivity  in  this  part  of  the 
nerve  may  make  difficult  the  demonstration  of 
irritability.) 

Minimal  and  Maximal  Stimuli  ;  Threshold  Value. 
—  Arrange  the  gastrocnemius  muscle  to  write  on 
a  smoked  drum.  Connect  one  binding  post  of 
the  secondary  coil  to  the  muscle  clamp,  the 
other  binding  post  to  the  post  on  the  muscle 
lever.  Load  the  muscle  with  10  grams.  De- 
scribe an  abscissa  on  the  smoked  paper,  turning 
the  drum  by  hand.  Send  a  feeble  break  induc- 
tion current  through  the  muscle. 

There  will  be  no  response. 

Repeat  the  break  currents,  gradually  moving 
the  secondary  closer  to  the  primary  coil. 


138      THE    PHYSIOLOGY   OF   MUSCLE   AND    NERVE 

At  a  certain  point  the  muscle  will  just  con- 
tract ("  threshold  value  ").  This  is  a  minimal 
contraction  produced  by  a  minimal  stimulation. 

Turn  the  drum  5  mm.,  move  the  secondary 
coil  5  mm.  nearer  the  primary,  send  in  another 
break  current,  and  record  the  contraction.  Con- 
tinue this. 

The  contraction  in  answer  to  each  break  cur- 
rent increases  with  the  strength  of  the  currents 
at  first  rapidly,  then  slowly,  up  to  a  certain  point. 
Further  increase  in  the  strength  of  the  stimulus 
produces  no  further  increase  of  contraction.  The 
stimulus  and  the  resulting  contraction  have  now 
become  maximal. 

There  is  a  striking  disproportion  between  the 
energy  of  the  stimulus  necessary  to  throw  a 
nerve  or  muscle  into  the  active  state,  and  the 
energy  that  the  stimulus  sets  free.  It  is  as  if  a 
spark  fell  into  powder ;  the  active  process  is  to 
be  regarded,  with  some  reservations,  as  an  explo- 
sion. But  only  a  part  of  the  latent  energy  of 
muscle  can  be  set  free  by  any  one  stimulus. 

Threshold  Value  Independent  of  Load.  —  Re- 
peat the  preceding  experiment,  and  load  the 
muscle  with  50  grams  instead  of  10. 

The  threshold  value  will  not  be  changed. 

Summation  of  Inadequate  Single  Stimuli.  — 
Place  the  secondary  coil  of  the  inductorium  at 


[SUITABILITY    AND   CONDUCTIVITY  139 

such  a  distance  from  the  primary  that  a  break 
current  shall  be  nearly,  but  not  quite  sufficient 
to  cause  a  contraction.  Let  the  muscle  rest 
without  stimulation  for  about  a  minute,  ltepeat 
the  inadequate  single  stimulation  at  intervals  of 
five  seconds.     No  curve  need  be  written. 

Alter  a  time,  contraction  will  be  secured. 

The  excitation  outlasts  the  stimulus,  and  rein- 
forces subsequent  stimuli :  finally,  the  summed 
excitations  call  forth  a  contraction.  Summation 
is  of  frequent  occurrence  probably  in  all  living 
tissues. 

Relative  Excitability  of  Flexor  and  Extensor 
Nerve  Fibres  ;  Ritter-Rollett  Phenomenon.  —  Ex- 
pose the  sciatic  nerve  in  a  brainless  frog  in 
the  pelvic  region.  Set  the  hammer  of  the  in- 
ductorium  in  action  (binding  posts  2  and  3), 
and  stimulate  the  nerve  with  weak  induction 
currents. 

The  leg  will  be  flexed. 

Use  stronger  induction  shocks. 

As  the  intensity  increases  extension  as  well  as 
flexion  is  seen.  A  still  further  increase  causes 
extension  only. 

The  gradations  of  intensity  necessary  to  show 
these  results  are  sometimes  difficult  to  secure. 
The  phenomenon  of  relative  excitability  is  not  lim- 
ited to  the  case  just  cited.     Weak  stimulation  of 


140       THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

the  vagus  causes  adduction  of  the  vocal  bands ; 
stronger  stimulation,  abduction.  Weak  stimula- 
tion causes  opening  of  the  claw  of  the  lobster,  while 
stronger  stimulation  of  the  same  nerve  causes  clo- 
sure. Weak  stimulation  of  the  hypoglossal  nerve 
in  the  dog  and  rabbit  causes  the  tongue  to  be  thrust 
from  the  mouth,  while  with  strong  stimulation  the 
tongue  is  withdrawn  into  the  mouth.  It  must  not 
be  forgotten  that  the  anatomical  nerves  stimulated 
in  these  experiments  are  composed  of  many  axis 
cylinders,  each  of  which  is  a  physiological  nerve. 
That  they  should  vary  in  excitability  is  to  be 
expected. 

A  second  and  probably  better  explanation  of 
the  Kitter-Eollett  phenomena  is  found  in  the  dif- 
ference in  structure  of  the  flexors  and  extensors. 
Muscle  fibres  consist  of  contractile  substance  im- 
bedded in  sarcoplasm.  The  relation  between 
the  contractile  substance  differs  in  the  same 
muscle  in  different  species  and  individuals,  and 
differs  further  in  the  muscles  of  the  same  indi- 
vidual. In  striated  muscles  of  vertebrates,  those 
rich  in  sarcoplasm  have  a  turbid,  opaque  appear- 
ance, while  those  poor  in  sarcoplasm  are  translu- 
cent. Important  differences  in  contractility, 
irritability,  etc.,  depend  on  this  difference  of 
structure.  Muscles  which  contain  many  "  clear  " 
fibres    (poor   in    sarcoplasm)  are   more   irritable 


IRRITABILITY  AND   CONDUCTIVITY  141 

than  those  containing  many  of  the  fibres  rich  in 
sarcoplasm.  In  the  flexors  of  the  frog  the  "  clear  " 
fibres  are  relatively  more  numerous  than  in  the 
extensors. 

Specific  Irritability  of  Nerve  Greater  than  that 
of  Muscle.  —  Arrange  an  inductorium  for  single 
induction  currents.  Make  as  rapidly  as  possible 
two  nerve-muscle  preparations,  A  and  B.  Bring 
a  wire  from  the  secondary  coil  to  each  end  of 
muscle  A.  Let  the  nerve  of  B  rest  on  muscle  A. 
No  stimulation  can  now  reach  B  except  through 
that  part  of  the  nerve  of  B  which  rests  on  muscle 
A.  Place  the  secondary  some  distance  from  the 
primary  coil.  Stimulate  muscle  A  with  make 
induction  shocks,  the  strength  of  which  is  gradu- 
ally increased  by  approximating  the  coils. 

Muscle  B,  which  is  stimulated  only  through 
its  nerve,  will  contract  before  muscle  A,  which 
is  stimulated  directly.  Hence,  the  specific  irri- 
tability of  nerve  is  greater  than  that  of  muscle, 
provided  (1)  that  the  intensity  of  the  stimulating 
current  is  equal  for  both  nerve  and  muscle,  and 
(2)  that  the  irritability  of  the  two  muscles  does  not 
differ,  and  (3)  that  the  stimulation  of  the  nerve 
of  B  is  not  by  unipolar  induction.  The  first 
source  of  error  may  be  excluded,  because  the 
density  of  the  current  passing  through  the  por- 
tion- of  nerve  lying  on  muscle  A  is  certainly  not 


142      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

greater  than  the  density  of  the  current  passing 
through  the  muscle  itself.  The  second  possibil- 
ity is  tested  as  follows  :  — 

Eeverse  the  muscles  and  repeat  the  experi- 
ment. 

The  result  will  not  be  altered. 

The  third  source  of  error  is  excluded  as  follows. 

Tie  a  ligature  about  the  nerve  of  B,  between 
muscles  A  and  B.  The  physiological  conduc- 
tivity of  nerve  B  is  thereby  destroyed,  and  the 
nerve  impulse  cannot  pass ;  but  the  physical  con- 
tinuity of  the  nerve,  and  hence  its  power  to  con- 
duct electricity,  is  still  present. 

The  strongest  induction  currents  applied  to 
muscle  A  will  now  fail  to  produce  contraction 
of  B. 

Irritability  at  Different  Points  of  Same  Nerve.  — 
Determine  the  threshold  value  for  the  sciatic 
nerve  near  the  gastrocnemius  muscle  and  about 
two  centimetres  from  the  cut  end  of  the  nerve. 

The  farther  from  the  muscle  the  nerve  is  stim- 
ulated, the  lower  will  be  the  threshold  value.  It 
has  been  suggested  in  explanation  of  this  that 
the  nerve  impulse  gathers  force  as  it  passes 
along  the  nerve,  and  is  the  more  powerful  the 
longer  the  nerve  which  it  traverses  (avalanche 
theory).  It  has  also  been  suggested  that  the 
nearer  to  the  nutrient  cell  of   origin  the  stim- 


IRRITABILITY   AND   CONDUCTIVITY  143 

ulus  is  applied,  the  greater  the  effect.  The  true 
explanation  lies  in  the  fact  that  the  irritability 
of  the  nerve  is  raised  in  the  neighborhood  of  the 
cross-section  by  the  passage  of  the  demarcation 
current  through  that  portion,  as  explained  on 
page  160.  Tigerstedt  has  shown  with  mechani- 
cal stimuli  that  the  uninjured  nerve  has  equal 
irritability  throughout. 

The  Excitation  Wave  remains  in  the  Muscle  or 
Nerve  Fibre  in  which  it  starts.  —  In  order  to 
limit  the  stimulus  to  one  or  two  fibres,  the 
method  of  unipolar  stimulation  may  be  adopted. 

Fasten  in  one  post  of  the  secondary  coil  of 
the  inductorium  arranged  for  tetanizing  currents 
a  wire  soldered  to  a  blunt  needle.  The  needle, 
except  near  the  free  end,  and  the  lower  part  of 
the  connecting  wire,  should  be  inclosed  in  a 
glass  tube  for  insulation. 

Expose  the  sacral  plexus  in  a  brainless  frog  in 
which  the  skin  has  been  removed  from  the  hind 
limbs.  Connect  the  preparation  by  means  of  a 
copper  wire  with  the  earth  through  the  gas  or 
water  pipes. 

Touch  the  sacral  nerves  here  and  there  with 
the  needle  electrode,  watching  meanwhile  the 
sartorius  muscle. 

Partial  contractions  will  be  seen  in  the  sar- 
torius,   now  of  the  inner,  now  the  outer  fibres, 


144      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

according   to  the   nerve   fibres   touched   by   the 
needle. 

Stimulate  the  sartorius  directly. 
Only  the  fibres  touched  by  the  needle  contract. 
Evidently  the  excitation  wave  remains  limited 
both  in  the  muscle  and  the  nerve  to  the  fibres  in 
which  it  starts. 

The  Same  Nerve  Fibre  may  conduct  Impulses 
both  Centripetally  and  Centrifugally.  —  1.  The 
nerve  of  the  sartorius  divides  at  the 
muscle,  part  going  to  each  half  of 
the  muscle  (Fig.  33).  Microscopical 
examination  shows  that  the  division 
is  not  simply  a  parting  of  individual 
nerve  fibres,  but  that  each  axis  cylin- 
der forks,  one  limb  going  upwards, 
Pig.  33.   The     the  other  downwards.     If  the  muscle 

sartorius. 

be  severed  between  the  forks,  no  im- 
pulse started  in  one  half  of  the  muscle  could  reach 
the  other  half,  except  by  going  up  one  branch  to 
the  original  axis  cylinder  and  down  the  remaining 
branch ;  for  it  is  known  that  the  nerve  impulse 
does  not  escape  transversely  from  one  axis 
cylinder  to  other  neighboring  ones. 

Eemove  a  sartorius  muscle  with  great  care. 
Split  the  muscle  in  the  middle  line  for  one  third 
of  its  length,  beginning  at  the  broad  end,  as  in- 
dicated in  the  diagram.     Stimulate  the  muscle 


IRRITABILITY   AND   CONDUCTIVITY  145 

fibres  of  the  right  segment  mechanically,  by 
snipping  the  preparation  with  scissors  in  the 
line  a.     Do  not  cut  cpiite  through  the  segment. 

Only  the  right  half  twitches. 

Eepeat  the  stimulus  by  snipping  in  the  line  ax 

Again  only  the  right  half  twitches. 

Stimulate  in  the  line  b. 

Both  segments  twitch,  or  at  least  some  fibres 
in  each. 

Eepeat  at  bv 

Both  segments  twitch  again. 

2.  The  gracilis  of  the  frog  is  divided  into  an 
upper,  shorter  part  and  a  lower,  longer  part  by 
a  tendon  (Fig.  34,  j).  Each  axis 
cylinder  in  the  nerve  iV,  on  ap- 
proaching the  muscle,  divides 
into  two  branches,  one  of 
which  goes  to  the  upper  and 
the  other  to  the  lower  portion 
of  the  muscle. 

Eeinove  the  muscle  together 
with  a  portion  of  its  attached  Pig-84,  The  gracilis- 
nerve,  and  examine  the  inner  surface  (Fig.  14). 
The  nerve  (iV)  divides  into  two  branches,  of 
which  the  upper  (A")  runs  to  the  shorter  portion 
of  the  muscle  and  is  unbranched  for  some  dis- 
tance, while  the  other  (Z)  has  a  very  short  stem 
and  sinks  almost  at  once  into  the  substance  of 
in 


146   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 


the  lower  part.     One  of  the  branches  (i7)  per- 
forates the  muscle  and  goes  to  the  skin. 

With  a  sharp  pair  of  scissors  cut  out  entirely 
the  part  shaded  in  the  diagram,  without  injuring 
the  nerves.  The  halves  of  the  muscle  are  now 
united  only  by  the  forked  nerve. 

Stimulate  the  end  branches  of   the  nerve   in 
one  of  the  pieces  of   muscle  by  snipping  with 
scissors  ;  also  chemically,  with  a  lump  of  salt. 
Both  pieces  will  contract. 

Speed  of  Nerve  Impulse.  —  Smoke  a  drum,  and 
adjust  it  for  "  spinning."    Place  two  pairs  of  non- 

polarizable  elec- 
trodes in  the  moist 
chamber.  Arrange 
the  inductorium  for 
maximal  make  cur- 
rents, placing  a  sim- 
ple key  and  the 
electromagnetic  sig- 
nal in  the  primary 
circuit  (Fig.  35).  Connect  the  secondary  coil  to 
the  side  cups  of  the  pole-changer.  Connect 
the  end  pairs  of  cups  each  with  one  pair  of 
the  electrodes  in  the  moist  chamber.  Make  a 
nerve-muscle  preparation,  preserving  the  full 
length  of  the  sciatic  nerve.  Fasten  the  femur 
in    the  clamp  in   the    moist  chamber.     Connect 


Fig.  35. 


IRRITABILITY    AND   CONDUCTIVITY  147 

the  Achilles  tendon  to  the  muscle  lever.  Bring 
the  point  of  the  lever  against  the  drum  imme- 
diately over  the  writing  point  of  the  electro- 
magnetic signal.  Let  the  nerve  rest  on  the 
electrodes,  one  pair  near  the  end  of  the  nerve, 
the  other  near  the  muscle.  Spin  the  drum 
slowly.  Hold  the  writing  point  of  a  vibrating 
tuning  fork  against  the  smoked  paper  beneath 
the  line  drawn  by  the  signal.  Send  a  maximal 
induction  current  through  first  one  pair  of  elec- 
trodes and  then  the  other.  Determine  the  inter- 
val between  the  moment  of  stimulation  and 
the  beginning  of  contraction  in  each  instance. 
[This  is  done  by  turning  the  drum  back  until 
the  writing  point  of  the  signal  lies  precisely  in 
the  vertical  line  marked  by  it  when  the  current 
was  made,  and  then  stimulating  the  muscle  to 
contract.  The  ordinate  drawn  by  the  muscle 
lever  (the  drum  being  still  at  rest)  will  be 
synchronous  with  the  ordinate  drawn  by  the 
signal  during  the  experiment.] 

It  will  be  found  that  the  interval  between 
stimulation  and  contraction  is  greater  when  the 
nerve  is  stimulated  far  from  the  muscle  than  it 
is  on  stimulation  near  the  muscle.  The  differ- 
ence is  the  time  occupied  by  the  passage  of  the 
excitation  wave  along  the  nerve  between  the 
electrodes. 


148   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

Measure  the  length  of  nerve  between  the  elec- 
trodes, and  calculate  the  speed  of  the  nerve  im- 
pulse per  second. 

It  is  assumed  in  this  method  that  the  interval 
between  the  closure  of  the  primary  circuit  and 
the  beginning  of  the  nerve  impulse  is  the  same 
in  both  instances,  and  that  the  interval  between 
the  arrival  of  the  impulse  in  the  muscle,  and  the 
visible  change  of  form,  is  likewise  the  same  in 
both.  If  the  mean  and  the  probable  deviation  of 
a  series  of  measurements  are  taken,  a  fairly  accu- 
rate result  may  be  expected.  A  better  method, 
however,  is  to  record  the  passage  of  the  negative 
variation  'over  a  measured  length  of  nerve  by 
photographing  the  meniscus  of  the  capillary 
electrometer.  Similar  measurements  can  be 
made  with  a  differential  rheotome  (page  176). 

Helmholtz  found  in  motor  nerves  of  the  frog 
an  average  speed  of  27  metres  per  second,  but 
the  individual  variation  is  considerable.  The 
speed  is  very  slow  compared  with  that  of  light,  or 
even  sound.  It  is  modified  by  changes  in  tem- 
perature, nutrition,  anaesthetics  (alcohol,  ether, 
chloroform,  carbon  dioxide),  the  intensity  of  the 
stimulus,  —  above  a  certain  value,  the  greater 
the  stimulus,  the  more  rapid  the  conduction,  — 
and  by  many  other  factors.  Specific  differences 
are   found  depending  on    the   structure   of   the 


IRRITABILITY   AND   CONDUCTIVITY  149 

nerve.  Thus  the  velocity  has  been  found  in 
mammalian  nerve  to  smooth  muscle  to  be 
about  9  metres  per  second,  while  in  the  bivalve 
Anodonta,  it  is  said  to  be  only  1  centimetre  per 
second. 

A PPARATUS 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate. 
Dry  cell.  Inductorium.  Key.  Wires.  Frog  with  sci- 
atic nerve  degenerated.  Hen's  egg  incubated  60-70  hours. 
NaCl  solution  (0.75%).  Ligatures.  Filter  paper.  One 
per  cent  solution  of  curare.  Pole-changer.  Gas  chamber. 
Carbon  dioxide  generator.  Twenty  per  cent  hydrochloric 
acid.  Broken  marble.  Alcohol.  Muscle  clamp.  Stand. 
Muscle  lever  with  scale  pan.  Millimetre  rule.  Five  to 
ten  gram  weights.  Needle  electrodes  (glass  tube).  Moist 
chamber.  Two  pairs  of  non-polarizable  electrodes.  Elec- 
tromagnetic signal.  Recording  drum.  Glazed  paper. 
Tuning  fork.     Normal  saline  clay. 


150      THE   PHYSIOLOGY   OF   MUSCLE  AND   NERVE 


VII 

THE  ELECTROMOTIVE   PHENOMENA   OF 
MUSCLE   AND   NERVE 

The  stored  energy  of  muscle  is  set  free  in 
molecular  movement,  —  heat,  chemical  action, 
and  electricity,  —  and  in  mechanical  work,  the 
change  in  form.  It  will  be  convenient  to  con- 
sider the  electromotive  phenomena  first. 

The  Demarcation  Current  of  Muscle 

Demarcation  Current  of  Muscle.  —  1.  Make  two 
non-polarizable  electrodes.  Connect  them  to  the 
capillary  electrometer  through  a  short-circuiting 
key.  Eemove  a  sartorius  muscle.  Cut  off  each 
end  with  a  sharp  knife  by  a  clean  cut  at  right 
angles  to  the  fibres.  Observe  that  the  muscle  is 
thereby  converted  into  a  "muscle  prism."  It 
possesses  two  artificial  cross-sections,  at  each  of 
which  the  muscle  has  been  injured,  and  is,  in 
fact,  dying,  and  an  uninjured  natural  longi- 
tudinal surface.  Place  one  of  the  non-polar- 
izable electrodes  against  a  cross-section  and  the 


THE   ELEOTKOMOTIVB   PHENOMENA  151 

other  on  the  middle  of  the  uninjured  longitudi- 
nal surface.  Bring  the  meniscus  of  the  capillary 
into  the  field.  Note  its  position  on  the  microm- 
eter scale.     Open  the  key. 

The  meniscus  will  be  displaced  in  the  direc- 
tion indicating  a  higher  potential  at  the  middle 
or  "  equator"  of  the  longitudinal  surface  than  at 
the  cross-section.  State  the  difference  of  poten- 
tial in  fractions  of  a  volt.  (The  electrometer  was 
calibrated  in  a  previous  experiment,  page  28). 

2.  Move  the  electrode  on  the  longitudinal  sur- 
face a  few  millimetres  towards  the  cross-section. 
Determine  the  difference  of  potential  here.  It 
will  be  less  than  before.  Measure  the  potential 
in  similar  manner  at  intervals  of  5  mm.  between 
this  point  and  the  cross-section.  On  co-ordinate 
paper  set  down  m\  the  abscissa  the  number  of 
millimetres  from  equator  to  cross-section.  Set 
down  as  ordinates  the  number  of  divisions  of  the 
micrometer  scale  traversed  by  the  meniscus  when 
the  electrode  on  the  longitudinal  surface  is  placed 
successively  on  the  equator,  and  at  intervals  of  5 
mm.  between  equator  and  cross-section.  Draw 
the  curve  uniting  the  summits  of  the  ordinates. 

As  the  cross-section  is  approached,  the  curve  of 
potential  will  fall  more  and  more  rapidly.  The 
centre  of  the  cross-section  is  negative  towards 
the  outer  parts  of   the  section.     Points  on  the 


152   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEKVE 

equator,  or  equidistant  from  it,  have  the  same 
potential.  Points  on  the  longitudinal  surface 
at  different  distances  from  the  equator,  and  on 
the  cross-section  at  different  distances  from  the 
centre  of  the  section,  show  a  slight  difference  of 
potential. 

Prove  these  several  statements. 

Oblique  Section.  —  When  the  artificial  cross- 
section  is  oblique  to  the  long  axis  of  the  muscle, 
the  maximum  difference  of  potential  is  no  longer 
at  the  equator  and  the  centre  of  the  cross-section. 
The  most  positive  point  is  on  the  longitudinal 
surface  near  the  obtuse  angle  made  by  the  oblique 
section,  and  the  most  negative  point  is  on  the 
cross-section  near  the  acute  angle.  The  structure 
of  certain  muscles,  the  frog's  gastrocnemius,  for 
example,  is  such  as  to  make  their  natural  cross- 
section  oblique.  In  consequence,  their  differ- 
ences of  potential  are  not  distributed  as  in  a 
regular  parallel-fibred  muscle  like  the  sartorius. 
In  the  gastrocnemius,  owing  to  the  peculiar  inser- 
tion of  the  muscle  fibres  into  the  tendon,  the 
upper  end  of  the  muscle  is  really  the  middle  of 
the  longitudinal  section,  while  the  lower  end 
is  the  acute  angle  of  an  oblique  cross-section. 
When  the  ends  are  connected  with  an  electrom- 
eter, a  strong  current  is  observed  flowing  (out- 
side the  muscle)  from  the  upper  to  the  lower  end. 


THE  ELECTROMOTIVE    PHENOMENA  153 

Uninjured  Muscle.  —  Prepare  a  sartorius  muscle 
with  extreme  care  to  prevent  injury.  Connect 
the  tendon  (the  natural  "cross-section")  and 
the  longitudinal  surface  with  the  electrometer 
through  a  short-circuiting  key.  Note  the  posi- 
tion of  the  meniscus  on  the  micrometer  scale. 
Open  the  short-circuiting  key. 

The  meniscus  will  move  but  little.  It  will  not 
move  at  all,  provided  the  muscle  has. not  been 
injured;  but  the  difficulty  of  preparation  is  such 
that  some  difference  of  potential  will  probably 
appear. 

Close  the  key.  Injure  the  muscle  by  drawing 
a  hot  wire  across  one  end.     Open  the  key. 

A  strong  demarcation  current  will  appear. 

Stimulation  by  Demarcation  Current.  —  1.  Make 
a  nerve-muscle  preparation  (sciatic  nerve  and 
gastrocnemius  muscle).  Let  the  nerve  near  the 
muscle  touch  a  cross-section  of  the  sartorius. 
Now  let  the  eud  of  the  nerve  fall  on  the  longi- 
tudinal  surface  near  the  equator. 

The  gastrocnemius  will  contract ;  the  nerve 
acts  as  a  conductor  between  the  positive  longi- 
tudinal surface   and  the  negative    cross-section. 

It  should  be  pointed  out  that  the  conclusion 
here  drawn  is  not  entirely  free  from  criticism. 
The  muscle  is  a  conductor  as  well  as  the  nerve, 
and  may  close  the  demarcation  current  of  the 


154   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

nerve,  as  the  nerve  may  close  that  of  the  muscle. 
Thus  it  is  possible  that  the  nerve  is  stimulated 
by  its  own  demarcation  current.  The  former 
explanation  is  the  more  probable. 

2.  Place  non-polarizable  electrodes  on  the 
longitudinal  surface  and  cross-section  of  the 
sartorius.  Fasten  the  wires  of  the  stimulating 
electrodes  in  the  binding  posts  of  the  non-polar- 
izable electrodes.  Drop  the  nerve  of  the  nerve- 
muscle  preparation  across  the  electrode  points. 

The  gastrocnemius  will  contract  when  the 
nerve  bridges  the  space  from  one  electrode  to 
the  other,  and  thus  completes  the  circuit  be- 
tween the  longitudinal  surface  and  cross-section 
of  the  sartorius. 

3.  Place  a  little  0.6  per  cent  solution  of  sodium 
chloride  in  a  porcelain  dish.  Fasten  one  end  of 
the  sartorius  gently  between  two  pieces  of  cork 
in  the  jaws  of  the  muscle  clamp.  Bring  the 
muscle  over  the  saline  solution.  Make  a  fresh 
clean  cross-section,  and  lower  the  clamp  on  its 
stand  until  the  cross-section  dips  (not  too  far) 
into  the  solution. 

The  muscle  will  twitch.  The  twitch  will  pull 
the  end  of  the  muscle  out  of  the  solution.  When 
the  muscle  relaxes,  the  contact  between  positive 
longitudinal  surface  and  negative  cross-section 
is  once  more  made  by  the  saline  solution,  the 


THE    ELECTROMOTIVE    PHENOMENA  155 

current  of  rest  flows  from  the  point  of  higher  to 
the  point  of  lower  potential,  and  again  stimulates 
the  muscular  tissue  through  which  it  passes. 
Thus  the  muscle  is  stimulated  by  its  own  cur- 
rent. A  long  series  of  contractions  may  be 
secured.  Other  liquid  conductors  will  serve. 
When  the  solution  touches  only  the  cross-sec- 
tion, there  is  no  contraction. 

4.  Prepare  a  fresh  sartorius  muscle  with  bony 
attachments.  Fasten  the  pelvic  end  in  the 
muscle  clamp.  Make  a  fresh  cross-section  in 
the  first  sartorius.  Hold  the  tibial  end  of  the 
second  muscle  in  such  a  way  that  the  muscle 
lies  horizontally  with  its  upper  surface  sonje- 
what  concave.  Against  this  surface  bring  the 
fresh  cross-section  of  the  first  sartorius.  The 
longitudinal  surface  will  naturally  also  touch 
to  some  extent. 

The  second  muscle  will  close  the  circuit  be- 
tween longitudinal  surface  and  cross-section  of 
the  first,  and,  if  very  irritable,  both  muscles  will 
contract. 

Interference  between  the  Demarcation  Current 
and  a  Stimulating  Current  ;  Polar  Refusal.  —  Con- 
nect a  dry  cell  through  an  open  key  with  the 
0  and  1  metre  posts  of  the  rheocord  (Fig.  36). 
Make  two  non-polarizable  electrodes,  and  con- 
nect them  through   a  pole-changer  (with  cross- 


156      THE    PHYSIOLOGY   OF   MUSCLE   AND   NERVE 


wires)  to  the  positive  post  and  slider  of  the 
rheocord.  Tie  a  thick  cotton  thread  to  the 
brush  of  the  positive  electrode  in  such  a  way 
that  the  thread  shall  hang  down  in  a  small  loop. 
Let  a  sartorius  muscle  rest  on  a  clean  glass 
plate.  Make  an  artificial  cross-section  by  draw- 
ing a  hot  wire  across  the  muscle  near  the  pelvic 
end.  Pass  the  loop  of  thread  on  the  positive 
electrode  over  the  muscle  about  5  mm.  from  the 
thermal  cross-section.  Let 
the  negative  electrode  rest 
on  the  cross  section.  Ar- 
range '  the  rheocord  for  weak 
currents.  Moisten  the  elec- 
trodes with  normal  saline 
solution.     Close  the  key. 

The  usual  closing  contraction 
will  be  absent  (polar  refusal). 
Note  that  the  galvanic  current  is  now  passing 
through  the  muscle  in  an  atterminal  direction, 
i.  e.  towards  the  injured  portion  (admortal),  while 
the  demarcation  current  is  passing  through  the 
muscle  in  the  opposite  direction.  The  two  cur- 
rents more  or  less  compensate  each  other.  Hence, 
the  absence  of  the  closing  contraction.  Observe, 
also,  that  opening  the  key  will  break  the  galvanic 
circuit,  but  that  the  circuit  for  the  demarcation 
current  will  still  be  closed  —  through  non-polar- 
izable  electrodes  and  rheocord. 


Pig.  36. 


THE   ELECTROMOTIVE   PHENOMENA  157 

Open  the  key. 

An  opening  contraction  will  take  place, 
obviously  because  the  muscle  current  is  no 
longer  compensated. 

Reverse  the  pole-changer,  so  that  the  anode 
lies  at  the  cross-section.  Open  and  close  the 
galvanic  current. 

Contraction  will  take  place  at  closure  only. 
The  electrode  -at  the  cross-section  again  refuses. 

Measurement  of  Electromotive  Force  of  Demar- 
cation Current.  —  1.  Prepare  a  sartorius  muscle, 
and  make  an  artificial  cross-section  near  the  pel- 
vic end.  Lay  one  non-polarizable  electrode  on 
the  cross-section,  the  other  on  the  equator.  Con- 
nect the  electrodes  to  the  capillary  electrometer 
through  a  short-circuiting  key  in  such  a  way  that 
the  capillary  shall  be  joined  to  the  electrode  which 
rests  on  the  cross-section  of  the  muscle.  Briner 
the  meniscus  into  the  field.  Note  the  position 
of  the  meniscus  on  the  micrometer  scale.  Note 
also  the  height  of  the  mercury  in  the  manometer. 
Open  the  key.  When  the  meniscus  has  come  to 
rest,  restore  it  to  its  original  position  by  turning 
the  pressure  screw.  Read  the  manometer  again, 
and  note  the  pressure  used  in  millimetres  of 
mercury.  Translate  this  into  fractions  of  a  volt 
by  means  of  the  graduation  scale  of  the  electrom- 
eter (page  29).     It  has  already  been  pointed  out 


158   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

that  in  the  capillary  electrometer  the  relation 
between  the  pressure  and  the  potential  must 
frequently  be  re-determined.  In  striated  frog 
muscle  the  electromotive  force  of  the  current  of 
rest  is  from  about  0.035  to  0.090  volt. 

2.    Compensation  Method.  —  The  electromotive 
force  of  a  current  of  injury  may  be  expressed  in 
fractions  of  a  Daniell  cell,  or  any  other  constant 
element,  by  bringing  into  the  same  circuit  with  the 
current  of  injury,  but  in  an 
opposite  direction,  so  much 
of  the  current  from  the  cell 
as  will  exactly  balance  the 
current   of   injury,  *'.  e.  so 
much  as  will  keep  the  menis- 
cus of  the  electrometer  from 
moving  in  either  a  positive 
or  negative  direction  when 
connected  with  the  circuit. 
Prepare  a  sartorius  muscle.     Connect  a  Daniell 
cell  with  the  0  and  10  metre  posts  of  the  rheocord. 
Connect  the  capillary  electrometer  to  a  closed 
short-circuiting  key.      From  the  post  joined  to 
the  capillary  lead  to  the  0  post  of  the  rheocord. 
Connect  the  remaining  post  of  the  key  to  a  non- 
polarizable  electrode  placed  on  the  cross-section  of 
the  muscle.     Join  the  slider  of  the  rheocord  to 
another  non-polarizable  electrode  placed  on  the 


THE    ELECTROMOTIVE    PHENOMENA  1  .r»9 

equator  of  the  muscle  (Fig.  37).  Bring  the  slider 
to  the  zero  post.  Bring  the  meniscus  into  the 
field.  Note  its  position  on  the  micrometer  scale. 
Open  the  short-circuiting  key.  When  the  me- 
niscus comes  to  rest,  move  the  slider  along  the 
rheocord  until  the  meniscus  returns  to  its  origi- 
nal position.  Read  the  number  of  millimetres 
between  the  positive  post  and  the  slider.  This 
number  divided  by  10,000  is  the  fraction  of  the 
electromotive  force  of  the  Daniel!  cell  (1.1  volt) 
necessary  to  balance  the  current  of  injury  of  the 
muscle. 

Demarcation-  Current  of  Nerve 

Place  non-polarizable  electrodes  on  the  cross- 
section  and  longitudinal  surface  of  a  long  piece 
of  sciatic  nerve.  Connect  the  electrodes  through 
a  short-circuiting  key  with  the  electrometer. 
Bring  the  meniscus  into  the  field  and  open  the 
short-circuiting  key. 

The  meniscus  will  move  in  a  direction  indicating 
a  current  in  the  nerve  from  cross-section  to  longi- 
tudinal surface,  as  in  muscle. 

Measure  the  electromotive  force  of  this  demar- 
cation current  (1)  directly  by  means  of  the 
electrometer,  (2)  by  the  compensation  method,  as 
described  above. 

The  demarcation  current  is  much  weaker  in 
nerve   than  in  muscle,  beino-  in  the   former  about 


160   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

0.025  volt,  as  against  about  0.060  volt  in 
muscle.  The  demarcation  current  of  muscle  is 
maintained  in  force  for  a  long  time,  whereas  that 
of  nerve  diminishes  rapidly.  The  nerve  current 
is  restored  on  making  a  fresh  cross-section. 

The  demarcation  current  from  the  cut  branches 
of  a  nerve  may  reach  electrodes  placed  on  the 
main  trunk,  and  thus  confuse  the  electrometer 
measurements.  To  this  same  cause  must  be 
ascribed  the  increased  irritability  observed  in  the 
main  trunk  in  the  neighborhood  of  branches ; 
the  irritability  is  raised  by  the  demarcation  cur- 
rent of  the  severed  branch. 

Nerve  may  be  stimulated  by  its  own  Demarca- 
tion Current.  —  On  a  glass  plate  make  a  U  shaped 
wall  of  normal  saline  clay,  each  limb  about  1  cm. 
long  and  3  or  4  mm.  wide.  Carefully  remove  the 
moisture  between  the  clay  walls  with  filter  paper. 
Lay  the  longitudinal  surface  of  the  nerve  of  a  nerve- 
muscle  preparation  on  one  limb  of  the  U,  and  with  a 
glass  rod  let  the  cross-section  fall  on  the  other  limb. 

When  the  circuit  between  the  cross-section  and 
the  longitudinal  surface  is  completed  by  contact 
with  the  clay,  the  demarcation  current  will 
stimulate  the  nerve,  and  the  resulting  nerve  im- 
pulse will  cause  the  muscle  to  contract. 

Other  Examples.  —  The  dropping  of  the  central 
end  of  the  severed  vagus  nerve  into  the  wound 
from  which  it  was  lifted  has  caus°d  the  slowing 


THE   ELECTROMOTIVE   PHENOMENA  161 

of  respiration,  presumably  by  the  stimulation  of 
the  nerve  through  the  closure  of  its  own  demar- 
cation current  by  the  lymph  or  blood,  though 
the  possible  influence  of  demarcation  currents 
from  the  wounded  tissues  cannot  be  forgotten. 
Definite  results,  such  as  inhibition  of  the  heart, 
have  not  been  observed  to  follow  the  closure  of 
the  current  of  the  peripheral  segment.  To  avoid 
any  chance  stimulation  from  the  closure  of  the  de- 
marcation current,  nerves  are  sometimes  severed 
physiologically  by  freezing,  —  a  process  which 
not  only  does  not  stimulate,  but  which  does  not 
destroy  permanently  the  conductivity  ;  the  latter 
returns  upon  the  restoration  of  the  nerve  to 
normal  temperature. 

The  olfactory  nerve  of  the  pike  shows  a  strong 
demarcation  current,  as  does  the  optic  nerve. 


Hypotheses  regarding  the  Causation  of 
the  Demarcation  Current 

Make  artificial  cross-sections  in  a  sartorius 
muscle,  and  test  the  difference  of  potential  be- 
tween the  longitudinal  surface  and  a  cross-section 
with  the  electrometer.  Divide  the  muscle,  longi- 
tudinally, and  make  fresh  cross-sections  ;  test  the 
difference  of  potential  again. 

However  small  the  muscle  prism  may  be 
11 


162   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

made,  the  longitudinal  surface  will  still  be  posi- 
tive to  the  cross-section. 

Molecular  Hypothesis.  —  The  fact  that  the 
smallest  possible  muscle  prism  is  still  positive 
on  the  longitudinal  surface,  and  negative  on  the 
cross-section,  suggested  to  DuBois-Keymond  that 
muscle  (and  nerve)  are  composed  of  electrical 
particles  or  molecules  something  like  the  mole- 
cules of  a  magnet.  A  magnet  has  two  poles, 
and,  however  it  may  be  divided,  the  pieces  still 


Pig.  38.    Scheme  of  the  myomeres  in  a  parallel-fibred  muscle  (Rosenthal). 


possess  a  north  and  a  south  pole.  The  magnet  is 
therefore  believed  to  be  composed  of  molecules, 
each  possessing  a  north  and  a  south  pole.  These 
molecules  lie  with  the  north  poles  all  pointing  in 
one  direction,  the  south  poles  in  the  other.  The 
structure  of  muscle  favors,  in  a  measure,  a  simi- 
lar hypothesis;  for  it  is  known  that  a  striated 
muscle  consists  of  fibrillse,  each  of  which  is  com- 
posed of  a  row  of  particles  arranged  in  quite 
regular  fashion.    The  electromotive  molecules,  or 


THE   ELECTROMOTIVE   PHENOMENA  163 

myomeres,  may  be  conceived  to  be  positive  on 
their  longitudinal  surfaces,  and  negative  on  their 
cross-sections  (Fig.  38).  They  are  assumed  to 
have  their  negative  surfaces  turned  towards  the 
ends  of  the  muscle  or  nerve,  and  the  positive 
equatorial  region  turned  towards  the  longitudi- 
nal surface.  A  non-electric  conducting  substance 
surrounds  them.  An  electrode  placed  on  the 
longitudinal  surface  would  touch  only  the  posi- 
tive sides,  while  an  electrode  placed  on  the  cross- 


Fig.  39.    Scheme  of  myomeres  in  an  oblique  section  (Rosenthal). 

section  would  touch  only  the  negative  poles. 
However  small  the  muscle  prism  was  made,  the 
relation  would  still  be  the  same.  Thus  the  dis- 
tribution of  potentials  would  correspond  with 
that  actually  observed. 

When  the  cross-section  is  oblique,  the  myo- 
meres at  the  cross-section  are  exposed  as  shown 
in  Fig.  39,  and  the  currents  which  pass  from  the 
longitudinal  surface  of  each  myomere  to  its  cross- 
section  are  added  tu  the  main  currents  passing 


164      THE   PHYSIOLOGY  OF   MUSCLE   AND   NERVE 

from  the  longitudinal  surface  to  the  cross-section 
of  the  whole  muscle.  The  region  of  maximum 
positive  potential  is  thereby  brought  towards  the 
obtuse  angle  of  the  oblique  cross-section,  and  the 
region  of  maximum  negative  potential  is  dis- 
placed towards  the  acute  angle,  as  actually 
observed. 

When  it  was  found  by  Bernstein,  Hermann, 
and  others,  that  uninjured  muscle  showed  no 
difference  of  potential,  DuBois-Keymond  as- 
sumed that  in  the  natural,  uninjured  state  the 
end  of  the  muscle  in  contact  with  the  tendon 
(the  "natural  cross- section  ")  is  composed  of  a 
layer  of  molecules  which  have  their  positive  in- 
stead of  negative  surface  turned  towards  the 
tendon. 

The  highly  artificial  and  complicated  structure 
which  DuBois  was  compelled  to  erect  on  this 
foundation  in  order  to  explain  all  the  electrical 
phenomena  of  living  tissue,  cannot  be  discussed 
here.  The  chief  argument  against  the  molecular 
theory  of  muscle  and  nerve  currents  is  that  the 
phenomena  can  be  explained  in  a  simpler  way. 

Alteration  Theory.  —  This  hypothesis,  in  the 
making  of  which  Hermann  and  Hering  have 
been  especially  active,  explains  the  electromo- 
tive forces  of  nerve  and  muscle  by  alterations  in 
the    chemical  composition  of  the  tissue  at  the 


THE    ELECTROMOTIVE    PHENOMENA  165 

cross-section.  When  the  cross-section  is  made, 
the  tissue  next  the  section  passes  through  the 
series  of  catabolic  changes  which  constitute 
muscle  death  ;  carbon  dioxide  is  given  off,  lac- 
tic acid  is  developed,  a  soluble  proteid  is  con- 
verted to  a  less  soluble  form,  etc.  The  contact 
of  this  dying  layer  with  the  uninjured  tissue  is 
believed  to  create  a  difference  of  potential.  The 
potential  difference,  therefore,  appears  at  the  de- 
marcation between  dying  and  uninjured  tissue, 
—  hence  the  term  "  demarcation  current."  The 
action  current  finds  its  explanation  in  the  chemi- 
cal changes  accompanying  contraction.  It  would 
be  interesting  to  consider  here  the  parallel  be- 
tween the  chemical  transformations  in  contrac- 
tion and  those  which  usher  in  the  death  of  the 
muscle,  but  we  must  be  content  with  mentioning 
the  apparently  close  relationship.  In  its  most 
general  form,  the  alteration  hypothesis  rests  on 
the  fact  that  living  substance  is  everywhere  the 
seat  of  constant  constructive  and  destructive 
changes.  Where  these  are  nearly  in  equilibrium, 
as,  for  example,  in  the  resting  uninjured  muscle, 
the  tissue  is  equipotential ;  where,  on  the  con- 
trary, either  form  of  chemical  change  has  the 
upper  hand,  as  in  the  explosion  which  we  term 
contraction,  and  in  dying  muscle,  it  is  assumed 
that  a  difference  of  potential  is  created. 


166   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

For  many  years  the  weight  of  physiological 
opinion  has  been  largely  on  the  side  of  the  alter- 
ation hypothesis ;  but  it  would  be  unsafe  without 
further  evidence  to  decide  finally  against  the 
molecular  theory. 

Action  Current  of  Muscle 

The  demarcation  current  (current  of  injury, 
current  of  rest)  just  studied  has  been  shown  to 
be  due  to  the  injury  of  the  tissue.  We  have 
now  to  examine  the  electromotive  forces  which 
appear  when  a  nerve  or  muscle  becomes  active. 

1.  Rheoscopic  Frog.  —  Make  two  nerve-muscle 
preparations,  A  and  B.  Let  the  nerve  of  B 
rest  on  muscle  A.  Stimulate  the  nerve  of  A 
with  single  induction  shocks,  and  with  the 
tetanizing  current. 

Muscle  B  will  contract  once  for  each  contrac- 
tion of  A.  The  current  of  action  of  muscle  A 
stimulates  the  nerve  of  B. 

Secondary  contraction  can  take  place  also  from 
muscle  to  muscle,  but  only  under  circumstances 
that  suggest  increased  irritability,  as,  for  example, 
through  partial  drying.  No  secondary  contrac- 
tion has  been  secured  from  voluntary  muscular 
contraction. 

2.  That  the  stimulus  to  the  nerve  of  the  rheo- 
scopic muscle  is  really  an  electrical  current,  is 


THE    ELECTROMOTIVE    TIIENOMENA 


167 


shown  by  the  capillary  electrometer.  Place 
muscle  A  in  the  moist  chamber.  Make  two 
non-polarizable  electrodes,  substituting  for  the 
brush  a  piece  of  well-washed  candle-wick  an  inch 
long,  thoroughly  wet  with  soft  normal  saline 
clay.  Let  one  electrode  rest  on  the  tendon 
and  the  other  on  the  equator.  Lead  from  the 
non-polarizable  electrodes  through  a  closed  short- 
circuiting  key  to  the  capillary  electrometer  (the 


Fig.  40.    The  wheel  interrupter. 

tendon  should  be  connected  with  the  capillary). 
Lay  the  nerve  on  stimulating  electrodes.  Connect 
the  latter  with  the  secondary  coil  of  an  indue- 
torium  arranged  for  single  induction  currents. 
Place  the  wheel  interrupter  (Fig.  40)  in  the  pri- 
mary circuit.  Bring  the  meniscus  into  the  field. 
Open  the  short-circuiting  key.  The  meniscus  will 
be  displaced  by  the  demarcation  current.  When 
the  meniscus  has  come  to  rest,  stimulate  the 
nerve  with  single  and  repeated  induction  currents. 


168   THE  PHYSIOLOGY  OP  MUSCLE  AND  NERVE 

With  each  stimulus  there  will  be  a  negative 
variation  (action  current)  of  the  demarcation 
current. 

When  the  number  of  stimuli  per  second  passes 
a  certain  point,  which  differs  with  different  in- 
dividuals, the  hitherto  separate  excursions  of  the 
meniscus  will  be  fused,  and  a  gray  blur  will 
appear  at  the  end  of  the  vibrating  column. 
Movements  of  this  rapidity  may  of  course  be 
studied  by  photographing  them  on  sensitive 
paper  moving  rapidly  enough  to  draw  the  fused 
image  out  into  a  line  in  which  its  component 
oscillations  are  each  distinct,  or  they  may  be 
observed  directly  by  the  stroboscopic  method. 

The  Action  Current  in  Tetanus  ;  Stroboscopic 
Method.  —  1.  If  a  piece  of  thin  black  paper  about 
1  cm.  square  is  fastened  vertically  on  the  end  of 
the  electromagnetic  signal  lever,  and  the  signal 
placed  in  the  primary  circuit  of  the  inductorium 
arranged  for  tetanizing  currents,  the  piece  of 
paper  will  move  each  time  the  primary  current 
is  made  or  broken  by  the  vibrating  hammer  of 
the  inductorium.  The  movement  is  so  rapid  that 
the  paper  seems  stationary  and  a  gray  haze  appears 
on  its  upper  and  lower  border. 

Connect  the  electrometer  with  the  secondary 
coil  of  the  inductorium,  and  bring  the  vibrating 
meniscus  into  the  field. 


THE   ELECTROMOTIVE    PHENOMENA  169 

Bring  the  stroboscopic  paper  next  the  acid 
reservoir  of  the  electrometer  at  such  a  height 
that  the  edge  of  the  meniscus  shall  be  seen 
through  the  gray  blur.  The  meniscus  will  no 
longer  appear  blurred,  but  will  be  as  sharp  as 
if  the  mercury  were  stationary.  This  appearance 
is  produced  only  when  the  stroboscopic  paper 
and  the  object  seen  by  its  aid  have  the  same 
periodicity  of  vibration.  If  the  periodicity  of 
the  vibrations  is  unequal,  interference  results, 
and  from  this  interference  the  rate  of  vibration 
of  the  observed  body  can  be  calculated.  For 
example,  if  the  observed  body  shows  three 
vibrations  per  second,  when  observed  through  the 
stroboscope,  its  rate  is  three  more  per  second  than 
that  of  the  stroboscope. 

In  the  present  instance,  the  meniscus  remains 
apparently  at  rest.  The  number  of  action  cur- 
rents is  therefore  identical  with  the  number  of 
stimuli. 

2.  Rheoscopic  Muscle  Tetanus. — The  same 
method  may  be  applied  to  the  analysis  of  the 
rheoscopic  tetanus  in  the  rheoscopic  muscle. 

Place  two  nerve-muscle  preparations  in  the 
moist  chamber.  Lay  the  nerve  of  B  on  the 
muscle  of  A.  Place  the  non-polarizable  elec- 
trode threads  on  the  tendon  and  the  longitudinal 
surface  of  muscle  B,  and  connect  them  through  a 


170      THE    PHYSIOLOGY    OF   MUSCLE   AND   NEKVE 

short-circuiting  key  with  the  electrometer. 
Place  the  nerve  of  A  on  electrodes  connected  with 
the  secondary  coil  (the  coil  should  be  well  over 
the  primary).  Bring  the  meniscus  into  the  field, 
and  open  the  short-circuiting  key.  Place  the 
stroboscope,  still  in  the  primary  circuit,  near  the 
meniscus.     Tetanize  the  nerve  of  A. 

For  each  stimulus  received  from  nerve  A, 
muscle  A  contracts ;  the  contractions  are  so 
frequent  that  they  fuse  into  tetanus.     At  each 


Pig.  41. 

contraction  of  A,  its  current  of  action  stimulates 
the  nerve  of  B,  and  B  also  contracts.  At  each 
contraction  of  B,  the  action  current  displaces 
the  meniscus,  which  falls  therefore  into  very 
rapid  oscillation.  Observe  the  meniscus  through 
the  stroboscope.  It  will  seem  to  be  standing 
still. 

Thus  the  apparent  continuous  contraction  of 
muscle  B  is  in  reality  a  series  of  simple  con- 
tractions, as  stated,  corresponding  in  number  to 
the  make  and  break  currents  of  the  inductorium. 


THE    ELECTROMOTIVE    PHENOMENA  171 

For  each  contraction  there  is  one  action  current 
in  each   muscle. ] 

When  a  muscle  and  its  nerve  are  removed 
without  injury  to  the  muscle,  electrodes  placed 
on  the  latter  will  show  no  difference  of  potential, 
as  already  stated  (page  153).  Stimulation  of  such 
a  muscle  through  its  nerve  causes  a  current  of 
action  to  start  at  the  point  at  which  the  nerve 
enters  the  muscle  fibres.  The  contraction  wave 
begins  also  at  this  point,  as  may  be  shown  very 
beautifully  by  "fixing"  the  contraction  in  the 
muscles  of  certain  insects  by  plunging  the  con- 
tracting muscle  into  a  solution  which  arrests  and 
"  sets  "  the  fibre  instantly.  In  such  cases  fibres 
will  be  found  in  which  the  contraction  wave  is 
caught  at  its  beginning  in  the  neighborhood  of 
the  nerve  end-plate. 

The  action  current,  beginning  at  the  entrance 
of  the  nerve  into  the  muscle  fibre,  passes  in  both 
directions  along  the  fibre.  As  may  be  shown 
with  the  differential  rheotome,  or  by  photograph- 
ing the  meniscus  of  the  capillary  electrometer, 
the  current  is  diphasic.  In  the  first  phase,  the 
current  is  directed  away  from  the  nerve,  in 
the  second  phase,  towards  it.  In  extirpated 
muscle,  the  second  phase  is  much  weaker  than 

1  The  experiment  also  demonstrates  that  the  meniscus  has  no 
after  vibrations,  but  follows  unerringly  the  changes  of  potential. 


172      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

the  first.  In  normal  muscle  in  situ  (human 
muscle),  this  difference  or  decrement  does  not 
appear. 

The  direction  of  the  current  obtained  with 
the  electrometer  from  the  whole  muscle  is  de- 
termined by  the  position  of  the  electrodes  with 
reference  to  the  nerve  equator,  namely,  a  trans- 
verse line  drawn  at  the  mean  distance  from  the 
entrance  of  all  the  nerve  fibres.  Points  nearer 
the  equator  are  negative  to  points  further  away. 

Action  Current  of  Human  Muscle.  —  Cover 
the  brass  electrodes  with  cotton  saturated  with 
saline  solution,  and  connect  them  with  an 
inductorium  arranged  for  tetanizing  currents. 
Close  the  short-circuiting  key  of  the  second- 
ary coil.  Eeplace  the  brush  in  the  non-polar- 
izable  electrodes  with  a  piece  of  well  washed 
candle-wick  a  foot  long.  Saturate  the  wick  with 
zinc  sulphate  solution.  Place  one  of  these  elec- 
trodes around  the  forearm  near  the  elbow,  the 
other  around  the  wrist.  (The  nerve  equator  lies 
about  the  upper  third  of  the  forearm.)  Connect 
the  electrodes  through  a  short-circuiting  key 
with  the  capillary  electrometer.  Place  the  brass 
electrodes  over  the  brachial  plexus  in  the  axilla. 
Bring  the  meniscus  into  the  field.  Open  the 
short-circuiting  key  leading  to  the  electrometer. 
If  the  meniscus  is  displaced  by  a  skin  (secretion) 


THE   ELECTROMOTIVE   PHENOMENA  173 

current  bring  it  back  by  means  of  the  pressure 
apparatus.  Set  the inductorium  inaction.  Open 
the  short-circuiting  key  of  the  secondary  coil, 
thus  stimulating  the  nerves. 

The  meniscus  will  be  displaced  by  an  action 
current. 

Action  Current  of  Heart.  —  1.  Expose  the 
heart  of  a  frog  (page  75).  Lay  the  nerve  of  an 
irritable  nerve-muscle  preparation  on  the  beating 
ventricle. 

During  diastole,  the  rheoscopic  muscle  will  be 
quiet ;  at  each  systole,  it  will  contract. 

2.  Tie  a  cotton  thread  one  inch  long  about  the 
brush  of  each  non-polarizable  electrode,  and  let 
the  ends,  wet  with  normal  saline  solution,  rest  on 
the  beating  heart,  one  on  the  base,  the  other  on 
the  apex.  These  electrodes  will  follow  the  move- 
ments of  the  heart.  Connect  the  electrodes 
through  a  short-circuiting  key  to  the  electrom- 
eter. 

During  the  diastole,  the  meniscus  will  remain 
at  rest.  At  each  beat  of  the  ventricle,  the 
meniscus  will  move ;  first  in  a  direction  indicating 
that  the  base  is  negative  to  the  apex,  and  then 
in  the  opposite  direction.  The  action  current 
passes  over  the  heart  from  base  to  apex. 

These  experiments  show  not  only  that  there 
is  an  action  current  at  each  systole  of  the  heart, 


174      THE   PHYSIOLOGY   OF  MUSCLE  AND   NEEVE 

but  are  evidence  also  that  the  resting  heart 
muscle  is  iso-electric  (i.  e.  of  uniform  potential). 
The  Action  Current  precedes  the  Contraction.  — 
Eemove  the  heart,  including  a  portion  of  the 
great  veins.  Set  the  metal  heart-holder  (Fig.  42) 
on  the  base  of  the  iron  stand  and  place  the  heart, 
together  with  some  normal  saline  solution,  in  the 
spoon  of  the  holder.     Eest   the  upright  of   the 


Fig.  42.    The  heart-holder. 


straw  heart-lever  on  the  ventricle  (the  lever 
should  be  counterpoised  with  a  "  washer "  or 
other  weight).  Make  a  nerve-muscle  preparation. 
Fasten  the  femur  in  the  upper  side  of  the  muscle 
clamp,  at  right  angles  to  the  long  axis  of  the 
clamp.  Bring  the  latter  near  the  heart-holder,  so 
that  the  nerve  may  rest  on  the  ventricle.  Fas- 
ten the  tendon  Achilles  to  the  muscle  lever  by 
a  thread  which  passes  over  the    pulley  on  the 


THE    ELEOTBOMOTIVE    PHENOMENA  175 

axis  of  the  lever  before  being  secured  to  the 
lever.  Thus  the  muscle,  though  below  the  lever, 
will  pull  it  upwards  when  contraction  takes  place. 
Let  the  two  writing  points  be  in  the  same  ver- 
tical line.  Start  the  drum  at  rapid  speed.  Two 
curves  will  be  recorded :  one  by  the  contraction 
of  the  ventricle,  the  other  by  the  rheoscopic  mus- 
cle, stimulated  to  contract  by  the  action  current. 
The  contraction  of  the  rheoscopic  muscle  will 
slightly  precede  the  contraction  of  the  ventricle. 

Current  of  Action  of  Human  Heart.  —  Place 
normal  saline  solution  in  two  beakers.  In  each 
let  the  brush  of  a  non-polarizable  electrode  dip. 
Connect  the  electrodes  through  the  usual  short- 
circuiting  key  with  the  electrometer.  Bring  the 
meniscus  into  the  field.  Let  an  assistant  place 
a  finger  of  each  hand  in  the  saline  solution. 

When  the  short-circuiting  key  is  opened  the 
meniscus  will  be  displaced  by  the  skin  (secretion) 
current.  Careful  observation  will  show  also  a 
periodic  variation  synchronous  with  the  systole 
of  the  heart. 

The  diphasic  character  of  the  action  current  of 
the  heart,  shown  so  well  by  the  capillary  elec- 
trometer to  the  unaided  eye,  appears  even  more 
clearly  when  the  movements  of  the  meniscus  are 
recorded  by  projecting  them  on  a  quickly  moving 
photographic  plate.     By  photography,  too,  the  di- 


176   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 


phasic  character  of  the  action  current  in  the  more 
rapidly  contracting  skeletal  muscle  is  made  visible, 
and  the  form  of  the  action  current  wave  recorded. 
Before  the  capillary   electrometer   was  used  for 


Fig.  43.   Scheme  of  differential  rheotome. 

this  purpose,  the  differential  rheotome  of  Bern- 
stein was  employed.  This  celebrated  invention 
consists  of  a  wheel  which  revolves  at  uniform 
speed  and  carries  contacts  by  which  the  primary 
circuit  of  an  inductorium   and   a   galvanometer 


THE  ELECTROMOTIVE   PHENOMENA  177 

circuit  may  be  made.  By  means  of  the  incluc- 
torium,  the  muscle  is  stimulated  at  one  end. 
The  galvanometer  records  the  current  of  action 
by  means  of  electrodes  placed  at  the  other  end 
of  the  muscle.  The  position  of  the  galvanometer 
contact  on  the  wheel  can  be  shifted  nearer  to  or 
farther  from  the  stimulating  contacts ;  thus  the 
interval  between  stimulation  and  the  making  of 
the  galvanometer  circuit  may  be  chosen  at  will, 
and  the  electromotive  force  at  any  point  in  the 
action  wave  registered.  By  repeatedly  changing 
the  interval,  the  several  portions  of  the  wave 
can  be  investigated  successively,  and  the  results 
plotted.  With  Hermann's  rheotachygraph,  the 
whole  electrical  change  may  be  recorded  at  one 
time.  In  this  instrument  the  stimulating  con- 
tacts revolve  rapidly,  and  the  galvanometer  con- 
tact less  rapidly,  so  that  the  interval  between 
stimulation  and  the  closure  of  the  galvanometer 
continually  alters.  The  effect  of  the  electrical 
change  on  the  galvanometer  is  thus  prolonged  so 
that  the  galvanometer  mirror  is  able  to  follow  it. 
The  results  from  these  different  methods  agree 
in  showing  that  the  electrical  change  sweeps 
over  the  muscle  (and  nerve),  in  the  form  of  a 
wave  at  a  rate,  in  frog's  muscle,  of  about  three 
metres  per  second.  The  duration  of  the  wave 
is  from  0.0033  to  0.0040  second.     The  ascent  is 


178      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

quicker  than  the  descent.  The  latent  period  is 
probably  absent;  the  process  begins  as  soon  as 
the  stimulus  reaches  the  muscle.  The  electro- 
motive force  of  the  action  current  for  a  single 
contraction  of  the  frog's  gastrocnemius  is  about 
0.08  volt. 

Direct  stimulation  of  the  whole  of  a  normal  un- 
injured muscle  produces  no  action  current  what- 
ever, because  the  whole  muscle  becomes  active 
at  the  same  moment. 

Action  Current  of  Nerve 

1.  Negative  Variation.  —  Sever  the  nerve  of  a 
nerve-muscle  preparation  close  to  the  muscle, 
and  lay  the  nerve  in  the  moist  chamber  on  a 
glass  plate.  Place  non-polarizable  electrodes  on 
the  equator  and  on  one  cross-section,  and  lead 
them  through  a  short-circuiting  key  to  the  cap- 
illary electrometer.  Place  a  second  pair  of  non- 
polarizable  electrodes  near  the  other  cross-section 
of  the  nerve.  Connect  this  second  pair  to  the 
secondary  coil  of  an  inductorium.  Connect  the 
primary  coil  through  a  key  and  the  wheel  inter- 
rupter with  a  dry  cell.  Bring  the  meniscus  into 
the  field.  Open  the  short-circuiting  key.  The 
meniscus  will  be  displaced  by  the  demarcation 
current.  Stimulate  the  nerve  with  induction 
shocks  at  different  rates. 


THE    ELECTKOMOTIVE    PHENOMENA  179 

A  negative  variation  will  be  observed  each 
time  the  nerve  is  stimulated. 

2.  The  current  of  action  is  not  dependent  on 
the  electrical  stimulation,  but  is  an  expression  of 
the  changes  in  the  nerve  which  constitute  the 
nerve  impulse.  It  follows  mechanical  as  readily 
as  electrical  stimulation. 

Lead  to  the  capillary  electrometer  from  non- 
polarizable  electrodes  placed  on  the  longitudinal 
surface  and  cross-section.  Note  the  position  of 
the  meniscus.  Stimulate  the  nerve  mechani- 
cally by  snipping  the  end  with  the  scissors. 

There  will  be  a  negative  variation  as  before. 

Positive  Variation.  —  The  direction  of  the  cur- 
rent of  action  is  not  always  opposite  to  that  of 
the  demarcation  current.  Biedermann  obtained 
a  current  in  the  positive  direction  on  stimulating 
the  nerve  to  the  adductor  muscle  in  the  lobster. 
In  the  tortoise,  the  cardiac  auricle  may  be  cut 
away  from  the  sinus,  without  injury  to  the  cor- 
onary nerve,  which  in  this  animal  carries  to  the 
auricle  the  cardiac  fibres  of  the  vagus.  After 
this  operation,  the  auricle  and  ventricle  remain 
motionless  for  a  time.  In  a  heart  thus  prepared, 
Gaskell  made  a  thermal  cross-section  by  im- 
mersing the  tip  of  the  auricle  in  hot  water,  and 
led  the  demarcation  current  to  a  galvanometer. 
The  stimulation  of  the  vagus  in  the  neck  —  the 


180      THE   PHYSIOLOGY   OF  MUSCLE   AND   NERVE 

heart  still  resting  —  caused  a  marked  increase  in 
the  demarcation  current,  in  other  words,  a  posi- 
tive variation.  "No  visible  change  in  the  form  of 
the  heart  was  observed. 

Positive  After  Current.  —  Compensate  the  de- 
marcation current  of  nerve  by  the  method  de- 
scribed on  page  158.  When  compensation  is 
secured,  note  the  position  of  the  meniscus  on  the 
scale,  and  tetanize  the  nerve.  The  meniscus  will 
be  displaced  by  the  current  of  action.  Note  the 
direction  of  the  current.  Break  the  stimulating 
current.  The  meniscus  will  return  to  and  pass 
the  position  which  it  held  when  the  demarca- 
tion current  was  compensated,  showing  thus  a 
current  opposed  in  direction  to  the  action 
current. 

The  positive  after  current  is  absent  in  weak- 
ened or  fatigued  nerves. 

Contraction  secured  with  a  Weaker  Stimulus 
than  Negative  Variation.  —  Place  the  non-polariz- 
able  electrodes  on  the  longitudinal  surface  of  the 
nerve  of  a  nerve-muscle  preparation.  Connect 
them  through  the  usual  short-circuiting  key 
with  the  electrometer.  Bring  the  meniscus  into 
the  field.  Arrange  the  inductorium  for  break 
currents.  Place  the  secondary  coil  some  dis- 
tance from  the  primary.  Stimulate  the  nerve 
in  the  extrapolar  region.      Approach   the    coils 


THE    ELECTROMOTIVE    PHENOMENA  181 

until  the  threshold  value  is  reached  and  the 
muscle  contracts. 

At  the  threshold  value  of  muscular  contrac- 
tion, the  current  of  action  in  the  nerve  will  not 
yet  be  demonstrable.  The  coils  must  be  still 
nearer  together  before  the  action  current  be- 
comes visible. 

This  experiment  has  a  certain  suggestive 
value.  It  would  not,  however,  be  safe  to  con- 
clude from  it  that  the  action  current  is  not 
an  essential  part  in  the  passage  from  the  resting 
to  the  active  stage.  The  failure  to  recognize  the 
action  current  probably  lies  in  the  method. 

Current  of  Action  in  Optic  Nerve.  —  Place  two 
non-polarizable  electrodes  in  the  moist  chamber, 
and  connect  them  through  a  short-circuiting  key 
with  the  capillary  electrometer.  Remove  the 
eye  of  the  frog,  together  with  a  portion  of  the 
optic  nerve,  and  lay  the  preparation  on  a  glass 
slide  in  the  moist  chamber.  Bring  one  non- 
polarizable  electrode  against  the  edge  of  the 
cornea,  and  the  other  against  the  optic  nerve. 
Cover  the  electrodes  and  the  preparation  with  a 
black  pasteboard  box  or  other  opaque  screen  to 
shut  off  the  light.  Note  the  position  of  the 
meniscus  in  the  field  of  the  microscope.  Open 
the  short-circuiting  key.  A  demarcation  current 
from  the  injured  optic  nerve  to  the  cornea  will 


182      THE   PHYSIOLOGY   OF   MUSCLE   A2TD   NEEYE 

be  indicated.  Kemove  the  box  so  that  light  shall 
fall  on  the  retina. 

The  demarcation  current  will  undergo  a  nega- 
tive variation. 

Shut  off  the  light  by  replacing  the  box. 

There  will  now  be  a  positive  variation. 

Currents  of  action  have  also  been  demonstrated 
in  the  central  nervous  system.  Gotch  and 
Horsley  find  that  when  the  spinal  cord  of  the 
monkey  is  severed,  and  non-polarizable  electrodes 
are  applied  to  the  longitudinal  surface  and  the 
cross-section,  a  negative  variation  of  the  current 
of  injury  appears  whenever  the  cortex  of  the 
cerebrum  is  stimulated  in  the  neighborhood  of 
the  fissure  of  Eolando,  —  the  "  motor  "  region.  A 
considerable  degree  of  localization  in  the  cord  is 
possible.  It  may  be  shown  that  the  negative 
variation  from  the  motor  region  of  the  cortex 
descends  the  cord  chiefly  in  the  crossed  pyramidal 
tract, —  a  collection  of  white  fibres  in  the  lateral 
column  of  the  cord  near  the  gray  matter.  It  is 
known  from  pathological  evidence  that  the  nerve 
impulse  from  the  motor  cortical  cells  passes 
through  these  fibres,  and  the  demonstration  of 
their  negative  variation  justifies  the  hope  that 
this  method  may  be  useful  in  determining  the 
course  of  other  nerve  fibres  in  the  brain  and 
cord. 


THE    ELECTF. 

Errors   from  Unipolar   Stimulation.  —    . 

*.he  dang .  -'-polar 

induction    currents    eater     _ 
circuit  in  obserrat 
pillar  y  electi 

Place  a  nerve  in  the  moist  chamber.     Cm 
■.piliary  electrometer  thro    _ 
iug  key  with  non-]  -  placed  on 

ogitadina]  surface  and        —  about 

5  mm.  apart.     Let   a  wire   connected  with  one 
-     >ndary  coal  rest  ontli  .  ibout 

'2  cm.  from  the  non-  Open 

the  snort-circuiting    key.     When    the    me:    • 

un  in  action. 
It:  th*-1    :.  _'    the 

I  nearer  the  primary,  until  unipolar 
etfects  app 

'"RREXT 

Secretion    Current  from   Mucous    Membrane.  — 
sk  in  from  the  lower  jaw  of  a  frog,  the 
skull  of  which  has  -  care- 

metal  in  - 
or  with  firs  gments  of 

clay  L  cm.  square  anc1 

thick  on  the   g     -  -  .mp   near  the 


184  THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

cork.  Lay  the  denuded  jaw  on  the  glass,  and 
turn  the  tongue  forward  with  a  glass  rod  until 
the  tip  can  be  secured  in  the  clamp.  Avoid  all 
roughness.  The  normally  upper  surface  of  the 
tongue  will  now  rest  on  the  clay.  Bring  one 
non-polarizable  electrode  into  contact  with  the 
clay,  and  let  the  other  touch  the  upper  (normally 
lower)  surface  of  the  tongue.  Connect  the  elec- 
trodes through  an  open  key  with  the  capillary 
electrometer.  Bring  the  meniscus  into  the  field, 
and  note  its  position  on  the  micrometer  scale. 
Close  the  key. 

A  strong  difference  of  potential  will  be  shown. 
The  normal  under  surface  is  usually  positive 
towards  the  normal  upper  surface. 

The  difference  of  potential  thus  demonstrated 
is  probably  chiefly  due  to  secreting  glands  in  the 
mucous  membrane.  If  the  "secretion  current" 
is  compensated  after  the  general  compensation 
method  described  on  page  158,  and  the  glosso- 
pharyngeal nerve  then  stimulated,  the  electrom- 
eter will  show  an  electromotive  force,  in  a 
direction  opposite  to  the  original  difference  of 
potential,  —  in  other  words,  a  "  negative  variation." 

Negative  Variation  of  Secretion  Current.  —  Place 
a  frog  curarized  until  voluntary  motion  is  just 
paralyzed  back  uppermost  on  the  frog  board. 
Strip    the    skin    from    one    thigh,   and    expose 


THE   ELECTROMOTIVE    PHENOMENA  185 

the  sciatic  nerve  of  this  side.  Place  non-polar- 
izable  electrodes  on  the  bare  muscle  of  the 
thigh  and  on  the  skin  of  the  leg.  Connect  the 
electrodes  to  a  rheocord  arranged  for  compensa- 
tion by  the  bridge  method,  as  shown  in  Fig.  37. 
Place  the  capillary  electrometer  in  a  short  cir- 
cuit. Bring  the  meniscus  into  the  field,  and 
note  its  position.  Open  the  short-circuiting  key. 
Move  the  slider  along  the  wire  until  the  meniscus 
returns  to  its  original  position.  Now  stimulate 
the  sciatic  nerve  with  the  tetanizing  current. 

A  negative  variation  will  be  seen.  If  the  skin 
current  was  slight,  the  variation  may  be  positive. 

The  greater  part  of  the  skin  current  is  doubt- 
less a  secretion  current,  but  not  all.  Weak  cur- 
rents have  been  obtained  from  skin  devoid  of 
glands,  for  example,  the  eel's  skin.  Hermann 
attributes  this  current  to  the  degeneration  which 
accompanies  the  change  of  the  nucleated  cells  of 
the  corium  to  the  dead  scales  of  the  outer 
epidermis. 

A  strong  secretion  current  may  be  obtained 
from  the  skin  of  the  foot  (cat).  On  stimulation 
of  the  sciatic  nerve,  the  current  is  increased 
(positive  variation). 

In  the  submaxillary  gland,  the  hilus  is  positive 
to  any  point  on  the  external  surface  of  the  gland. 
Stimulation  of  the  chorda  tympani  nerve,  secre- 


186   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

tory  fibres  from  which  are  supplied  to  the  gland, 
causes  the  surface  to  become  still  more  negative, 
i.  e.  the  secretion  current  is  increased  (positive 
variation).  Stimulation  of  the  sympathetic,  which 
also  sends  fibres  to  the  gland,  causes  the  secretion 
current  to  lessen  (negative  variation). 

Electrotonic  Currents 

It  has  already  been  shown  that  the  irritability 
and  conductivity  of  the  nerve  are  altered  by  the 


Fig.  44. 

galvanic  current.     So  also  are  the  electromotive 
properties. 

Place  one  pair  of  non-polarizable  electrodes 
near  the  middle  of  a  long  piece  of  extirpated 
nerve,  and  one  other  pair  at  each  end,  on  the 
cross-section  and  longitudinal  surface  as  in  Fig. 
44.  Connect  the  middle  pair  through  a  key 
with  two  dry  cells.  Connect  each  of  the  other 
pairs    through  a    short-circuiting    key    with   a 


THE   ELECTROMOTIVE    PHBMOMKNA  187 

capillary  electrometer.  Let  one  observer  watch 
each  meniscus,  while  a  third  experimenter 
manages  the  polarizing  current.  Note  the  posi- 
tion of  each  meniscus.  Open  the  short-circuiting 
keys.  In  each  electrometer,  the  meniscus  will  lie 
displaced  by  the  demarcation  current.  It  should 
be  noted  that  the  demarcation  currents  are  of 
opposite  direction,  flowing  in  the  nerve  from  the 
cross-section  towards  the  longitudinal  surface. 
Make  the  polarizing  current. 

When  the  polarizing  current  enters  the  nerve, 
there  will  be  a  twitch  in  each  electrometer, 
caused  by  the  negative  variation  of  the  demar- 
cation current;  this  may  be  neglected.  Each 
meniscus  will  be  displaced;  on  the  side  of  the 
anode  of  the  polarizing  current,  the  demarcation 
current  will  be  reinforced,  but  on  the  side  of  the 
cathode  it  will  be  diminished. 

Thus  the  passage  of  the  galvanic  current 
through  a  part  of  the  nerve  has  polarized  the 
nerve  on  both  sides  of  that  part.  The  extra- 
polar  region  on  the  side  of  the  anode  becomes 
positive ;  the  extrapolar  region  on  the  side  of  the 
cathode  becomes  negative  ;  similar  changes  prob- 
ably occur  in  the  intrapolar  region.  In  short,  an 
electrotonic  current  is  set  up,  having  the  same 
direction  as  the  polarizing  current.  This  electro- 
tonic  current  augments  the  demarcation  current 


188   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEEVE 

on  the  side  of  the  anode,  but  is  opposed  to  that 
on  the  side  of  the  cathode.  It  appears  when 
any  two  points  on  the  longitudinal  surface  are 
"  led  off "  to  the  electrometer,  and  is  entirely 
independent  of  the  demarcation  current. 

The  intensity  of  the  electrotonic  current  de- 
pends on  the  intensity  of  the  polarizing  current. 
The  greater  the  separation  of  the  polarizing  elec- 
trodes, the  less  the  electrotonic  effect,  as  might  be 
expected  from  the  great  resistance  of  nerve.  If 
this  factor  be  excluded  by  placing  in  the  circuit 
a  much  greater  resistance  than  that  of  nerve,  the 
electrotonic  effect  will  be  found  to  increase  with 
the  length  of  the  intrapolar  region.  The  electro- 
tonic current  is  absent  in  dead  nerves,  in  strongly 
cooled  nerves,  and  in  those  ligated  between  the 
polarizing  electrodes  and  the  electrodes  leading 
to 'the  electrometer. 

In  muscle,  the  electrotonic  currents  are  much 
stronger  than  in  nerve. 

Negative  Variation  of  Electrotonic  Currents  ; 
Positive  Variation  (Polarization  Increment)  of  Polar- 
izing Current.  —  Place  the  polarization  electrodes 
near  one  end  of  the  nerve.  Connect  them  through 
a  short-circuiting  key  with  a  dry  cell.  From  the 
short-circuiting  key  lead  to  a  capillary  electrom- 
eter (Fig.  45).  From  the  middle  of  the  nerve 
lead  off  the  electrotonic  current  through  a  short- 


TILE   ELECTROMOTIVE   PHENOMENA 


189 


circuiting  key  to  a  second  capillary  electrometer. 
Near  the  other  end  of  the  nerve  place  stimu- 
lating electrodes  connected  with  the  secondary 
coil  of  an  inductorium  arranged  for  tetanization. 
Make  the  polarizing  current.  Open  the  short- 
circuiting  key  leading  to  the  electrotonic  elec- 
trometer, and  note  the  position  taken  by  the 
meniscus  under  the  influence  of  the  electrotonic 
current.      Make  the  tetanizing  current. 


45. 


The  strength  of  the  electrotonic  current  will 
be  diminished.  At  the  same  time  the  strength 
of  the  polarizing  current  will  be  increased  (polar- 
ization increment). 

These  are  in  reality  action  currents. 

The  electrotonic  currents  are  absent  in  nerves 
which  lack  a  myelin  sheath.  This  suggests  that 
the  myelin  in  some  way  divides  the  nerve  into  a 
core  and  a  sheath.  If  a  zinc  wire  connecting 
two  electrodes  is  surrounded  by  a  layer  or  sheath 


190      THE   PHYSIOLOGY   OF   MUSCLE   AND   NEEVE 

of  saturated  solution  of  sulphate  of  zinc,  there 
will  be  no  polarization,  and  the  current  will  not 
spread  to  any  extent  beyond  the  electrodes.  If, 
however,  the  wire  is  platinum  instead  of  zinc, 
polarization  will  take  place  where  the  current 
passes  from  the  electrodes  through  the  electrolyte 
into  and  out  of  the  wire,  and  the  polarization 
may  be  recognized  by  connecting  the  extrapolar 
region  with  the  electrometer  as  in  the  foregoing 
experiment.  The  resistance  to  the  spread  of  the 
electrotonic  current  in  a  longitudinal  direction  is 
relatively  slight,  so  that  it  passes  almost  instantly 
along  the  core. 

In  nerve,  also,  the  greater  resistance  in  the 
transverse  direction  (five-fold  greater  than  the 
resistance  in  the  longitudinal  direction)  would 
favor  the  spread  of  electrotonic  currents  length- 
wise along  the  nerve. 

Certain  observations  of  Biedermann  make  it 
difficult  to  accept  without  reservation  the  simple 
physical  explanation  just  offered.  For  example, 
the  narcotization  of  a  nerve  with  ether  or  chloro- 
form causes  the  electrotonus  to  disappear  a 
short  distance  from  the  electrodes,  although 
still  strongly  present  in  their  immediate  neigh- 
borhood. These  experiments  cannot  be  discussed 
here,  but  they  indicate  that  to  the  purely  physi- 
cal must  be  added  a  physiological  electrotonus. 


THE   ELECTROMOTIVK   PHENOMENA  191 

The   Electrotonic    Current  as   a  Stimulus.  —  As 

would  naturally  be  expected,  the  electrotonic 
current  may  be  an  effective  stimulus.  Bring  the 
end  of  an  extirpated  nerve  A  into  contact  with 
the  distal  portion  of  the  nerve  of  a  nerve-muscle 
preparation,  B,  as  in  Fig.  46,  and  place  on  the 
other  end  of  A  non-polarizable  electrodes  joined 
through  a  key  to  a  battery  of  two  cells.  Make 
the  galvanic  current. 

Muscle  B  will  contract. 

The  galvanic  current  polarizes  nerve  A,  and 
the  electrotonic  current  thereby 
set  up  passes  into  the  nerve  of    ^v--~5) — Q 
B  through  the  contact,  and  occa-    V  r 
sions    in    nerve    B    an    impulse     ()  (j 
which    descends    to    the    muscle 

Big.  u\. 

and  stimulates  it  to  contract. 

Paradoxical  Contraction.  —  Expose  the  bifur- 
cation of  the  sciatic  nerve  into  tibial  and  peroneal 
bvanches.  Polarize  either  of  these  branches. 
(The  electrodes  should  not  be  placed  too  near 
the  bifurcation.) 

On  making  and  breaking  the  polarizing  cur- 
rent, the  muscles  supplied  by  each  branch  will 
contract. 

In  this  instance,  the  extrapolar  region  of  the 
branch  polarized  lies  in  part  in  the  main  trunk. 
The  electrotonic  current  there  spreads  into  the 


192   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

contiguous   axis   cylinders,   among    them    those 
of  the  other  branch. 


Electric  Fish 

There  are  several  species  of  fish  which  possess 
the  power  of  discharging  electrical  currents  when 
stimulated.  The  best  known  are  Torpedo,  a  ray 
found  on  the  coasts  of  Europe  ;  G-ymnotus,  the 
electrical  eel  of  South  America ;  and  Malapteru- 
rus  electricus,  a  catfish  found  in  the  Nile  and 
other  African  rivers.  The  electromotive  force  of 
these  fishes  is  derived  from  a  special  organ  placed 
beneath  the  skin.  This  electrical  organ  is  bilat- 
eral and  is  formed  of  parallel  plates.  One  side 
of  each  plate  receives  a  branch  of  the  electrical 
nerve,  which  in  Malapterurus  is  a  single  great 
axis  cylinder  derived  from  a  giant  nerve  cell. 
The  side  of  the  plate  receiving  the  nerve  becomes 
negative  to  the  other  side  when  the  electrical 
organ  is  active  ;  it  behaves  like  the  negative  plate 
of  the  ordinary  cell.  When  the  nerve  is  at  rest, 
there  is  no  difference  of  potential  in  the  electrical 
organ.  The  discharge  in  the  active  state  is  peri- 
odic, and  may  rise  to  200  per  second.  The  elec- 
tromotive force  is  considerable :  in  Torpedo,  30-35 
volts,  5  volts  for  each  cubic  centimetre  of  the 
organ,  0.08  volt  for  each  plate.     The  fish  itself 


THE   ELECTROMOTIVE   PHENOMENA  193 

is  not  injured  by  the  current ;  its  tissues  are 
not  easily  excitable  by  electricity,  though  they 
respond  readily  to  mechanical  stimulation. 

Apparatus 

Normal  saline.  BowL  Towel.  Pipette.  Glass  plate. 
Sharp  knife.  Two  dry  cells.  Four  non-polarizable  elec- 
trodes. Simple  key.  Capillary  electrometer.  Co-ordi- 
nate paper.  Millimetre  scale.  Inductorium.  Electrodes. 
Thirteen  wires.  Porcelain  dish.  Muscle  clamp.  Muscle 
lever.  Stand.  Cork.  Rheocord.  Normal  saline  clay. 
Filter  paper.  Wheel  interrupter.  Candle-wick.  Electro- 
magnetic signal.  Pole-changer.  Bent  hooks.  Black  paper 
(stroboscope).  Moist  chamber.  Large  and  small  brass 
electrodes.  Cotton.  Common  salt.  Two  beakers.  Satu- 
rated solution  of  zinc  sulphate.  Cotton  thread.  Frog 
board.  Heart-holder.  Black  box  for  covering  retina. 
Bunsen  burner.     Glass  slide.     Cork  clamp.     Frogs. 


194      THE    PHYSIOLOGY    OF   MUSCLE   AND    NERVE 


VIII 

THE   CHANGE  IN  FORM 

The  change  in  form  or  the  contraction  of  muscle 
is  the  most  conspicuous  of  the  several  ways  in 
which  its  energy  is  set  free.  It  has  already  been 
shown  that  this  change  consists  of  a  shortening 
of  the  contractile  mass  followed  by  a  return  to 
the  original  length.  It  is  necessary  now  to  de- 
termine whether  the  muscle  becomes  smaller  on 
entering  the  active  state  or  whether  the  altera- 
tion in  form  is  simply  a  shifting  —  a  transloca- 
tion —  of  the  muscular  units. 

Volume  of  Contracting  Muscle 

Strip  the  skin  from  the  hind  limb  of  a  frog. 
Hang  the  limb  from  the  hooked  electrode  in  the 
stopper  of  the  volume  tube  (Fig.  47)  and  place 
the  stopper  loosely  in  the  tube.  Hook  the  elec- 
trode at  the  other  end  of  the  tube  into  the  limb 
near  the  foot.  Fill  the  tube  absolutely  full  of 
boiled  normal  saline  solution,  slightly  withdraw- 
ing the  stopper  for  the  purpose.  Eeplace  the 
stopper  in  the  tube  in  such  a  way  that  all  air 


THE    CHANGE    IN    FORM 


195 


bubbles  shall  be  excluded.     If  the  height  of  the 

water-column  in  the  capillary  tube 

does  not  permit  the  meniscus  to  Le 

readily  observed,  move  the  glass  rod 

in  the  stopper  in  or  out  until  the 

meniscus  is  adjusted.     Connect  the 

electrodes  with  the  secondary  coil 

uf    an     inductoriuin    arranged    fur 

single    induction    currents.       Note 

carefully  the  level  of  the  water  in 

the  capillary  tube.     Stimulate  the 

muscle     with     a     maximal     break 

current. 

The   level   of   the  water   in    the 
capillary    will    not    change.      The 
change  in   the  form  of  the  contracting  muscle 
is  not  accompanied  by  a  change  in  volume.1 


Pig.  -17.    The 
volume  tube. 


The  Single  Contraction  or  Twitch 

The  change  in  the  form  of  the  muscle  on 
entering  the  active  state  is  usually  studied  from 
the  graphic  record  made  on  a  smoked  surface 
by  a  writing  lever  the  shorter  arm  of  which  is 
attached  to  the  end  of  the  muscle.  Such  a 
record,  it  should  be  remarked,  gives  the  extent 

1  This  experiment  must  not  be  regarded  as  excluding  a  very 
slight  change  in  volume,  because  of  the  difficulty  of  expelling, 

by  boiling  or  otherwise,  all  the  air  iu  the  saline  solution. 


196      THE   PHYSIOLOGY    OF   MUSCLE   AND   NERVE 

and  the  time  relations  of  the  shortening,  but  not 
the  thickening  of  the  muscle.     (See  page  202.) 

The  Muscle  Curve.  Prepare  a  gastrocnemius 
muscle  together  with  the  distal  third  of  the 
femur.  Fasten  the  latter  in  the  muscle  clamp. 
Attach  the  tendo  Achillis  to  the  hook  on  the 
muscle  lever  by  means  of  a  fine  copper  wire 
which  should  be  wrapped  round  the  hook  and 
the  end  then  carried  to  the  binding  post  on  the 
muscle  lever.  Place  a  ten-gram  weight  in  the 
scale-pan.  Connect  the  posts  on  the  clamp  and 
the  lever  with  the  secondary  coil  of  an  inducto- 
rium  arranged  for  maximal  induction  currents. 
In  the  primary  circuit  place  an  electromagnetic 
signal.  Bring  the  writing  points  of  the  signal 
and  the  muscle  lever  against  the  smoked  paper 
in  the  same  vertical  line.  Start  the  drum  at  its 
most  rapid  speed.  Stimulate  the  muscle  with  a 
maximal  break  current. 

The  muscle  will  shorten  and  then  extend, 
marking  a  period  of  rising  energy  and  a  period 
of  sinking  energy.  Note  that  the  period  of  rising 
energy  is  shorter  than  the  period  of  sinking 
energy.  Close  observation  will  show  that  the 
lever  does  not  begin  to  move  at  the  instant  the 
muscle  is  stimulated,  —  there  is  here  an  interval 
or  latent  period. 

The  Duration  of  the  Several  Periods.  —  Turn  to 


THE   CHANGE    IN    FORM  197 

the  right  the  screw  at  the  top  of  the  sleeve  bear- 
ing the  recording  drum  until  the  sleeve  is  raised 
from  the  friction  bearing.  The  drum  can  now 
he  "spun."  Start  the  tuning  fork  vibrating, 
spin  the  drum,  lay  the  writing  point  of  the  tun- 
ing fork  on  the  smoked  paper  near  the  line 
traced  hy  the  electromagnetic  signal,  and  stim- 
ulate the  muscle  with  a  maximal  induction 
current. 

An  interval  will  be  found  between  the  moment 
of  stimulation  (marked  by  the  electromagnetic 
signal)  and  the  beginning  of  contraction.  This 
interval  is  the  mechanical  latent  period.  Meas- 
ure its  duration  by  means  of  the  tuning  fork 
curve.  Measure  also  the  duration  of  the  period 
of  rising  energy  and  the  period  of  sinking  energy. 

Helmholtz,  who  first  measured  the  latent  period 
of  frog's  muscle,  found  a  mean  duration  of  0.01 
sec,  while  the  phase  of  rising  energy  measured 
0.04  sec,  and  the  phase  of  sinking  energy  0.05 
sec.  More  recent  measurements  by  Tigerstedt 
and  others  have  reduced  the  latent  period 
given  by  Helmholtz  to  from  0.0025  to  0.005 
sec  The  interval  observed  grows  less  as  the 
intensity  of  stimulation  is  increased  from  the 
threshold  to  the  maximal  value;  further  in- 
crease in  intensity  (supermaximal  stimulation) 
causes  no  further  diminution  in  the  latent  period. 


198   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

The  period  is  shorter  at  high  temperatures  than 
at  low,  with  maximal  break  induction  currents 
than  with  make  induction  currents,  with  break 
induction  currents  than  with  closure  of  the  gal- 
vanic current.  Changing  the  load  of  the  muscle 
is  without  effect  on  the  latent  period. 

When  the  muscle  is  stimulated  through  its 
nerve  the  latent  period  is  longer  by  about  0.002 
sec.  than  when  the  electrodes  are  placed  on  the 
muscle  itself  (Bernstein),  due  allowance  being 
made  for  the  time  occupied  by  the  passage  of 
the  nerve  impulse  along  the  trunk  of  the  nerve 
from  the  point  of  stimulation  to  the  muscle.  The 
additional  time  is  taken  perhaps  in  the  passage 
of  the  impulse  through  the  end  plate  into  the 
contractile  substance. 

Griitzner  has  shown  that  the  striated  muscle 
fibres,  particularly  of  vertebrates,  differ  in -their 
histological  elements.  Some  are  rich  in  sarco- 
plasm,  and  when  seen  by  transmitted  light  appear 
cloudy  and  granular;  others  have  less  sarcoplasm 
and  are  relatively  translucent.  This  difference 
in  structure  is  associated  with  a  striking  differ- 
ence in  the  character  of  the  contraction.  The 
muscles  composed  chiefly  of  turbid  fibres  contract 
slowly,  while  "  clear "  muscles  contract  rapidly 
(compare  page  140).  Thus  in  the  rabbit  the 
duration  of  the    contraction    of  the   red   soleus 


THE   CHANGE    IN   FORM  199 

muscle,  which  is  rich  in  sarcoplasm,  is  about 
1.0  sec,  while  in  the  white  gastrocnemius — a 

"clear"  muscle — it  is  0.25  sec.  In  the  frog,  the 
contraction  period  of  the  hyoglossus  is  0.205, 
the  gastrocnemius  0.120,  and  the  gracilis  0.108 
sec.  (Cash).  The  latent  period  is  longer  in  the 
red  muscles.  The  amplitude  of  contraction  is 
less  in  the  red  than  in  the  white. 

The  mixture  of  quickly  and  slowly  contracting 
fibres  in  the  same  muscle  is  sometimes  obviously 
an  advantage.  Thus  in  certain  bivalves  the  quick 
fibres  in  the  shell-closing  muscle  close  the  shell 
rapidly,  and  the  slow  fibres  keep  it  closed  after 
the  contraction  of  the  quick  fibres  has  ceased. 

The  form  of  the  contraction  is  influenced  by 
the  mixture  of  fibres.  The  clear  fibres  reach 
their  maximum  shortening  sooner  than  those 
rich  in  sarcoplasm.  In  some  instances,  indeed, 
the  contraction  curve  may  show  two  summits. 
These  differences  may  perhaps  explain  the  char- 
acteristic differences  in  the  form  of  the  contrac- 
tion  wave  of  different  muscles,  observed  by  Cash 
and  others.  The  white  fibres  are  more  easily 
fatigued  than  the  red.  Thus  the  triceps  humeri 
of  the  rabbit  contracts  at  the  beginning  of  stimu- 
lation like  an  unmixed  white  muscle  (quickly), 
but  later  like  a  red  muscle  (slowly). 

The  Excitation  Wave.  —  Secure  the  cork  clamp 


200      THE    PHYSIOLOGY    OF   MUSCLE   AND   NERVE 

(Fig.  17)  in  the  muscle  clamp.  Smoke  a  drum. 
Eaise  the  drum  off  the  friction  bearing  by  turning 
to  the  right  the  milled  screw  at  the  top  of  the 
shaft.  Fasten  a  curarized  sartorius  muscle  to 
the  cork  block*  on  the  upper  margin  of  the  cork 
clamp 1  by  means  of  two  needles  to  the  ends  of 
which  conducting  wires  are  soldered.  Let  the 
cork  clamp  compress  the  muscle  sufficiently  to 
prevent  the  passage  of  a  contraction  wave  from 
one  part  of  the  muscle  to  the  other,  but  not  suffi- 
ciently to  prevent  the  passage  of  the  excitation. 
Let  a  second  pair  of  needle  electrodes  rest  on  the 
muscle  near  the  upper  side  of  the  cork  clamp. 
Connect  the  two  pairs  of  electrodes  to  the  end 
cups  of  a  pole-changer  (without  cross  wires),  the 
side  cups  of  which  are  connected  with  the  secon- 
dary coil  of  an  inductorium  arranged  for  single 
maximal  induction  currents.  In  the  primary 
circuit  of  the  inductorium  place  the  electro- 
magnetic signal.  Fasten  the  tibial  end  of  the 
muscle  to  a  muscle  lever.  Bring  the  writing 
point  against  the  smoked  surface  exactly  under- 
neath the  point  of  the  electromagnetic  signal. 
"Spin"  the  drum  slowly.  Place  the  writing 
point  of  a  vibrating  tuning  fork  against  the 
smoked  paper  below  the  recording  levers.     Stim- 

1  This  cork  block  has  been  omitted  from  Fig.  17  for  the  sake 
of  clearness. 


THE   CHANGE   IN   FORM  201 

ulate  the  muscle  with  ;i  maximal  break  current 
first  tli rough  one  pair  of  electrodes  and  then 
through  the  other.  En  each  of  the  resulting 
curves  measure  the  interval  between  stimulation 
and  contraction  (for  method  s.ee  page  147). 

This  interval  will  be  longer  when  the  muscle 
is  stimulated  farther  from  the  portion  the  con- 
traction of  which  is  recorded.  The  difference  is 
the  time  taken  by  the  excitation  to  traverse  the 
part  of  the  muscle  lying  between  the  two  pairs 
of  electrodes.  Measure  the  distance  and  calcu- 
late the  speed  of  the  excitation. 

The  nature  of  the  excitation  process  is  un- 
known. The  current  of  action  has  been  shown 
to  precede  the  visible  change  in  form  of  muscle. 
It  is  usually  assumed  to  be  a  manifestation  of  the 
excitation  process,  but  the  precise  relation  between 
the  two  has  never  been  ascertained.  The  speed 
of  the  excitation  is  the  same  as  that  of  the  con- 
traction wave. 

The  Contraction  Wave.  —  Fasten  a  CUrarized 
gastrocnemius  muscle  upon  the  glass  plate  of  the 
cork  clamp  by  means  of  two  needle  electrodes  at 
the  end  bearing  the  cork  block,  and  by  means  of 
an  ordinary  pin  at  the  other  end.  The  cork 
clamp  should  be  supported  on  the  wooden  stand. 
Attach  a  small  piece  of  cork  to  the  double  hook 
on  two  counterpoised   muscle   levers,   each    sup- 


202      THE    PHYSIOLOGY    OF   MUSCLE   AND   NERVE 

ported  on  a  separate  stand.  Let  the  cork  pieces 
rest  respectively  on  the  muscle  near  the  femur 
and  the  Achilles  tendon.  Bring  the  writing 
points  of  the  two  levers  against  a  smoked  drum 
in  the  same  vertical  line.  Let  a  tuning  fork 
write  its  curve  near  that  of  the  muscle  levers. 
Set  the  tuning  fork  vibrating.  Let  the  drum 
revolve  rapidly.  Stimulate  the  muscle  at  one 
end  with  a  maximal  make  induction  current. 

The  lever  near  the  point  of  stimulation  will 
begin  to  rise  before  that  farther  away.  Evidently 
the  contraction  starts  at  the  point  stimulated  and 
spreads  along  the  muscle  in  the  form  of  a  wave 
(compare  pages  171  et  seq.). 

Determine  the  speed  per  second  of  the  wave 
of  contraction  by  measuring  with  the  tuning  fork 
curve  the  time  occupied  by  the  wave  in  passing 
along  the  muscle  from  one  lever  to  the  other. 

It  is  evident  that  a  lever  resting  on  a  horizontal 
muscle  will  register  the  change  in  form  of  the 
cross-section  on  which  the  lever  lies,  while  a  lever 
attached  to  the  end  of  a  muscle  suspended  verti- 
cally will  be  moved  by  the  change  in  form  of  all 
the  cross-sections  of  which  the  muscle  is  com- 
posed. The  curves  secured  by  the  two  procedures 
are  similar  in  form,  but  different  in  duration. 
The  curve  of  thickening  is  shorter  by  the  differ- 
ence between  the  time  taken  by  the  contraction 


TIIK   CHANGE    IN    FOBM  2U3 

wave  to  pass  over  the  single  cross-section,  on  the 
one  hand,  and  the  whole  length  of  the  muscle  on 
the  other. 

An  extirpated  muscle  is  apt  to  remain  shortened 
after  contraction.  To  bring  muscles  back  to  their 
original  length  it  is  usually  necessary  to  weight 
them,  or  —  as  in  the  body  —  to  submit  them  to 
the  pull  of  antagonists.  Even  the  weighted 
muscles  may  return  very  slowly  and  imperfectly 
to  their  normal  length.  This  contracture,  as  it  is 
termed,  is  seen  especially  in  strong  direct  stimu- 
lation, in  poisoning  with  veratrine,  and  as  death 
comes  on.  Contracture  is  not  the  result  of 
fatigue,  for  when  the  muscle  is  repeatedly 
stimulated  contracture  diminishes,  instead  of 
increasing.  During  contracture,  the  irritability 
of  the  muscle  for  stimulation  through  the  nerve 
is  diminished. 

Relation  of  Strength  of  Stimulus  to  Form  of 
Contraction  Wave.  —  Fasten  the  femur  of  a  gas- 
trocnemius preparation  in  the  muscle  clamp  and 
attach  the  Achilles  tendon  to  the  muscle  lever 
with  a  fine  copper  wire  the  end  of  which  should 
be  carried  to  the  binding  post  on  the  handle  of 
the  lever.  Connect  this  post  and  that  on  the 
muscle  clamp  with  the  secondary  coil  of  the  in- 
ductorium.  Bring  the  writing  point  against  the 
smoked  drum.     .Stimulate  the  muscle  with  break 


204   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEKVE 

induction  currents  of  varying  intensity  and  record 
the  contraction  curves. 

It  will  be  found  that  the  contraction  is  longer 
with  weak  stimuli  than  with  strong. 

Influence  of  Load  on  Height  of  Contraction.  — 
Attach  a  curarized  gastrocnemius  preparation 
to  the  muscle  lever  and  bring  the  writing  point 
against  a  smoked  drum.  Connect  the  binding 
posts  on  the  lever  and  the  muscle  clamp  with 
the  secondary  coil  of  the  inductorium.  Load 
the  muscle  with  the  lever  and  scale-pan  only. 
With  the  drum  at  rest  record  the  contraction 
on  stimulation  with  a  maximal  induction  current. 
Turn  the  drum  by  hand  one  millimetre.  Place 
a  one-gram  weight  in  the  scale-pan,  and  record 
the  contraction  produced  by  a  make  induction 
current  of  the  same  intensity  as  before.  Con- 
tinue to  add  gram  weights  and  to  record  the 
contractions  until  ten  one-gram  weights  have 
been  placed  in  the  scale-pan.  Transfer  the 
muscle  to  the  rigid  lever  (Fig.  48).  Now  in- 
crease the  load  each  time  by  ten  grams,  record- 
ing the  contraction  after  each  increase,  until  the 
muscle  is  weighted  with  one  hundred  grams. 
(Care  should  be  taken  not  to  fatigue  the  muscle 
by  stimulating  it  oftener  than  is  necessary  to 
obtain  the  record.) 

Within  certain  narrow  limits  the  height  of  the 


THE   CHANGE    IN    POEM 


205 


contraction  will  be  increased  l>y  the  increase  in 
the  load.  With  increasing  loads  the  height  of 
contraction  diminishes 
at  first  quickly,  and 
then   more  slowly. 

Influence   of   Temper- 
ature on  the  Form  of  the 

Contraction.  —  Prepare 
a  gastrocnemius  muscle 
together  with  its  attach- 
ment to  the  femur. 
Fasten  the  femur  in  the 
clamp  on  the  under  side 
of  the  cover  of  the 
"  muscle  warmer  "  (Fig. 
49).  Tie  the  end  of  a 
fine  copper  wire  about 
ten  centimetres  long 
around  the  Achilles  ten- 
don. Fasten  the  other 
end  of  the  wire  to  a  split 
lead  shut.  Bring  the 
shot  through  the  open- 
ing in  tin1  bottom  of  the 
muscle  warmer  and 
wrap  the  wire  around 
the  hook  of  the  muscle 
lever.     Remove  the  shot  and  fasten  (he  end  to 


Pig.  18.    The  ri^rid  muscle  lever, 
with  removable  isometric  spring. 


206      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

which  it  was  attached  in  the  binding  post  on  the 
muscle  lever.    Make  sure  that  the  wire  connecting 


Fig.  49.    The  "  muscle  wanner  "  ;  an  apparatus  for  studying  the  in- 
fluence of  temperature  on  muscular  contraction. 

the  tendon  with  the  muscle  lever  is  vertical.  Con- 
nect the  binding  posts  of  the  muscle  warmer  and 
the  muscle  lever  with  the  secondary  coil  of  an  in- 


Till'.   CHANGE    IN    FORM  207 

ductorium  arranged  for  single  induction  currents. 
Pill  the  chamber  of  the  muscle  wanner  with 
cracked  ice.  Bring  the  writing  point  of  the 
muscle  lever  against  a  smoked  drum.  Let  the 
drum  revolve  at  fairly  rapid  speed.  Stimulate 
the  cooling  muscle  at  intervals  of  5°  with  a 
maxima]  break  current. 

Note  that  as  the  temperature  falls  the  contrac- 
tion curve  becomes  longer.  The  phase  of  rising 
energy  is  lengthened  more  than  the  relaxation. 
The  earlier  portion  of  the  relaxation  is  lengthened 
less  than  the  later;  the  muscle  shows  a  tendency 
to  contracture  (see  page  203). 

Place  fresh  paper  on  the  drum.  Let  the  drum 
revolve  very  slowly.  Place  a  lighted  Bunsen 
burner  under  the  arm  of  the  muscle  warmer.  At 
intervals  of  5°  stimulate  the  muscle  with  a  maxi- 
mal break  current.  Note  the  changes  in  the 
contraction. 

The  height  of  contraction  is  least  at  the  freezing 
point  of  the  muscle  (-5°).  It  rises  from  the 
freezing  point  to  0°;  falls  from  0J  to  19°;  in- 
creases to  30°,  which  is  the  maximum;  from  30° 
to  45°  diminishes  again  ;  and  at  4f>°  the  frog's 
muscle  usually  enters  into  a  state  called  rigor 
caloris ;  the  muscle  becomes  opaque,  inelastic, 
resistant  to  the  touch, shortens  very  considerably, 
and  undergoes  chemical  changes  of  great  impor- 


208   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

tance.  The  duration  of  contraction  lessens  with 
the  rising  temperature,  being  least  at  30°.  Above 
30°  the  duration  remains  approximately  un- 
changed. The  latent  period  is  increased  at  low 
temperatures,  diminished  at  high.  Above  30°  the 
excitability  to  electrical  stimuli  diminishes  stead- 
ily ;  it  disappears  almost  entirely  before  rigor  is 
reached. 

Influence  of  Veratrine  on  the  Form  of  the  Con- 
traction.—  With  a  capillary  pipette  inject  in  the 
dorsal  lymph  sac  5  drops  of  a  1  per  cent  solution 
of  veratrine  sulphate  or  acetate.  After  a  few 
minutes  test  for  symptoms  of  veratrine  poisoning 
by  pinching  the  foot  from  time  to  time. 

Soon  the  mechanical  stimulation  will  be  fol- 
lowed by  prolonged  contraction  of  the  extensor 
muscles  and  still  more  prolonged  relaxation. 

Make  a  gastrocnemius  muscle  preparation. 
Fasten  the  muscle  to  a  muscle  lever  and  bring  the 
writing  point  against  a  smoked  drum.  Eecord  a 
single  contraction. 

Note  the  increased  height  of  the  phase  of 
shortening,  and  the  prodigious  increase  in  the 
duration  of  the  phase  of  relaxation.  This  con- 
tracture (page  203)  is  lessened  by  repeated  stimu- 
lation, but  reappears  if  the  muscle  be  allowed 
to  rest.  Cooling  or  warming  usually  causes  the 
veratrine  effect  to  disappear  temporarily. 


THE    CHANCE    IN    FORM  209 

A  quick  initial  contraction  may  precede  the 
characteristic  veratrine  contraction,  possibly  he- 
cause  the  veratrine  affects  differently  the  red  and 
the  clear  fibres. 

Tetanus 

Superposition  of  Two   Contractions.  —  Arrange 

a  gastrocnemius  muscle  to  write  on  a  smoked 
drum.  Connect  the  binding  posts  on  the  muscle 
lever  and  muscle  clamp  with  the  secondary  coil 
of  an  inductormm.  In  the  primary  circuit  (posts 
1  and  2)  place  the  electromagnetic  signal  and  the 
wheel  interrupter.  Let  the  drum  revolve  at  a 
rapid  rate.  Send  two  maximal  induction  cur- 
rents through  the  muscle  at  varying  intervals, 
beginning  with  the  shortest  interval  possible. 
The  secondary  should  be  at  such  a  distance  from 
the  primary  coil  that  both  make  and  break  cur- 
rents shall  cause  contraction. 

If  the  second  stimulus  fall  in  the  latent  period 
of  the  first  contraction,  the  stimulus  will  be  with- 
out effect.  If  the  second  stimulus  fall  between 
the  beginning  of  shortening  and  the  end  of  relax- 
ation caused  by  the  first  stimulus,  the  contraction 
following  the  second  stimulus  will  not  begin  from 
the  base  line,  but  will  be  superposed  on  the  first, 
as  if  the  state  of  shortening  from  which  the 
second  contraction  begins  were  the  resting  stage 
of    the    muscle.      The    height   reached    by   the 

14 


210   THE  PHYSIOLOGY  OF  MUSCLE  A.ND  NERVE 

second  contraction  will  be  greater  than  that 
reached  by  the  first.  The  summed  height  is 
usually  greatest  when  the  second  contraction 
starts  from  the  summit  of  the  first,  but  this  rule 
is  not  invariable.  The  summit  of  the  summed 
contraction  does  not  necessarily  coincide  with  the 
summit  of  the  second  contraction ;  the  higher  the 
summed  contraction,  the  quicker  the  summit  is 
reached. 

Superposition  in  Tetanus.  —  Repeat  the  pre- 
ceding experiment,  but  use  a  series  of  stimuli 
instead  of  only  two.  It  will  be  observed  that 
a  third  contraction  may  be  superposed  on  the 
second,  a  fourth  on  the  third,  and  so  on.  The 
shortening  of  muscle,  however,  has  a  limit ;  and 
when  this  is  reached,  further  stimulation  merely 
maintains  this  maximum  degree*  of  shortening 
until  fatigue  sets  in.  Observe,  too,  that  when  the 
interval  between  successive  stimuli  is  so  brief 
that  the  period  of  shortening  of  each  successive 
contraction  begins  before  the  shortening  of  the 
preceding  contraction  has  ceased,  the  respective 
periods  of  shortening  fuse  together  and  the  con- 
traction curve  becomes  a  continuous  line.  In 
addition  to  the  proof  just  furnished  that  this 
apparently  continuous  single  contraction  is  really 
a  fusion  of  many  individual  contractions,  the 
reader   is   reminded   of   the  proof  furnished   by 


THE    CHANGE   IN   FORM  211 

the  action  currents  in  tetanus  (page  1G8).  The 
more  rapid  the  contraction,  the  shorter  must  be 
the  interval  between  successive  stimuli  in  order 
to  cause  the  phase  of  shortening  of  each  con- 
traction to  fall  in  the  shortening  of  the  pre- 
ceding contraction.  Thus  a  more  rapid  rate  of 
stimulation  is  necessary  to  produce  complete 
fusion  in  fresh,  highly  irritable  muscles  than  in 
those  the  irritability  of  which  has  been  diminished 
by  cold  or  fatigue.  For  this  reason  contractions 
which  at  the  beginning  of  the  stimulation  period 
are  marked  by  notches  in  the  curve  fuse  com- 
pletely as  longer  stimulation  brings  on  fatigue. 
Here  also  the  differences  in  the  structure  of 
muscles  already  mentioned  play  an  important 
part.  Thus  the  red  muscles  of  the  rabbit  are 
thrown  into  tetanus  by  a  much  smaller  number 
of  stimuli  per  second  than  are  the  more  quickly 
contracting  white  muscles. 

Muscle  Sound.  —  The  discontinuous  nature  of 
tetanic  contraction  is  further  borne  out  by  the 
sound  given  forth  by  contracting  muscle. 

1.  Stop  each  ear  with  the  finger  and  contract 
the  muscles  of  the  jaws. 

A  very  low-pitched  musical  sound  will  be  per- 
ceived. It  apparently  corresponds  to  the  C  of  32 
vibrations  or  the  D  of  36.  The  experiment  is 
best  performed  during  the  quiet  of  the   night. 


212      THE   FHYSIOLOGY   OF   MUSCLE   AND   NERVE 

2.  Stop  the  ears  and  contract  the  biceps  of 
each  arm. 

The  sound  will  again  be  heard.  It  is  trans- 
mitted to  the  internal  ear  by  sympathetic  vibra- 
tions set  up  in  the  bones  of  the  arm,  shoulder, 
neck,  and  head. 

3.  Listen  with  a  stethoscope  to  the  sound  of 
the  masseter  or  the  forearm  muscles. 

The  mechanism  of  this  sound  was  revealed  by 
the  observations  of  Helmholtz.  Within  limits, 
the  sound  obtained  from  a  muscle  in  tetanus 
rises  in  pitch  as  the  rate  of  stimulation  increases. 
It  may  be  assumed,  therefore,  that  the  muscle 
sound  is  the  result  of  the  periodic  contractions 
of  the  muscle ;  in  other  words,  that  the  volun- 
tary contraction,  since  it  gives  rise  to  a  sound, 
is  a  series  of  single  contractions  following  each 
other  at  fairly  regular  intervals. 

As  the  sound  observed  lies  very  near  the 
lowest  rate  of  vibration  perceptible  to  the  human 
ear,  it  may  be  suspected  that  it  is  not  really 
the  fundamental  note,  but  an  overtone,  and 
this  idea  is  confirmed  by  the  following  experi- 
ment. 

4.  Place  a  very  thin  easily  vibrating  reed  in 
the  jaws  of  a  clamp.  Fasten  on  the  end  a  tinsel 
writing  point.  Bring  the  point  against  a  smoked 
drum.     Let  a  tuning  fork  write  its  curve  beneath 


THE   CHANGE    IN    FORM  213 

the  point,  Set  the  reed  vibrating  and  "spin" 
the  drum.  Count  the  vibrations.  If  they  are 
not  18  per  second,  shorten  or  lengthen  the  reed 
until  this  rate  is  attained.  Make  a  gastrocne- 
mius preparation.  Fasten  the  femur  in  the 
muscle  clamp  and  pass  a  thread  attached  to  the 
tendo  Achillis  around  the  base  of  the  vibrator. 
Connect  the  two  ends  of  the  muscle  with  the 
secondary  coil  of  an  inductorium.  To  the  arma- 
ture of  the  electromagnetic  signal  turned  upside 
down  fasten  a  straw  36  centimetres  long.  About 
22  centimetres  from  the  magnet,  pass  vertically 
through  the  straw  a  platinum  wire  connected  by 
a  very  thin  wire  with  one  of  the  binding  posts  of 
the  magnet.  Connect  the  other  binding  post  with 
post  1  of  the  inductorium.  Place  the  magnet  so 
that  the  platinum  wire  shall  touch  the  surface 
of  the  mercury  in  the  mercury  cup  when  the 
straw  vibrates.  Connect  this  cup  through  a 
simple  key  and  a  dry  cell  to  post  2  of  the 
primary  coil.  On  closing  the  key,  the  straw 
will  be  kept  in  continued  vibration.  The  rate 
should  be  brought  to  18  per  second  by  varying 
the  length  of  the  straw.  Now  start  the  inter- 
rupter and  open  the  short-circuiting  key  of  the 
secondary  coil. 

The   muscle   will  fall  into  tetanus.     The   dis- 
continuous  nature  of  the  tetanus  will  be  shown 


214   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 

by  the  vibration  of  the  reed  at  the  rate  of  18  per 
second,  corresponding  to  the  number  of  stimuli 
per  second. 

It  also  appears  from  this  experiment  that  the 
note  of  about  36  vibrations  per  second  heard  on 
auscultating  a  contracting  muscle  is  not  the 
fundamental  tone  itself,  but  the  first  overtone 
of  the  muscle  sound. 

5.  The  pitch  of  the  sound  heard  when  a 
muscle  is  thrown  into  tetanus  by  stimulating 
the  spinal  cord  is  to  a  considerable  extent  in- 
dependent of  the  rate  of  stimulation. 

•  Lengthen  the  vibrating  reed  used  in  Experi- 
ment 4  by  moving  it  out  from  the  jaws  of  the 
clamp,  so  that  the  reed  shall  vibrate  about  10 
times  per  second. 

Expose  the  vertebral  column  in  a  frog  the  brain 
of  which  has  been  destroyed  (page  132).  Strip 
the  skin  from  one  leg.  Free  the  lower  end  of  the 
gastrocnemius  muscle  by  severing  the  tendon. 
Eaise  the  muscle  so  that  it  may  be  attached  to 
the  under  side  of  the  vibrating  reed  mentioned 
in  Experiment  4,  but  be  careful  not  to  injure 
the  nerve.  Insert  needle  electrodes  between 
the  vertebrae  and  connect  them  with  the  secon- 
dary coil  of  an  inductorium  arranged  for  teta- 
nizing  currents  (posts  2  and  3).  Stimulate  the 
muscle. 


THE   CHANGE    IN    FORM  215 

The  reed  will  again  be  thrown  into  sympa- 
thetic vibration,  although  the  number  of  stimuli 
is  about  LOO  per  second. 

With  the  aid  of  the  interrupter  described  in 
Experiment  4  stimulate  the  spinal  cord  at  the 
rate  of  18  per  second. 

The  vibrations  during  tetanus  will  be  stronger. 
Helmholtz  found  that  they  were  strongest  at  18 
stimulations  per  second,  from  which  he  concluded 
that  voluntary  tetanus  was  occasioned  in  the  frog 
by  the  discharge  of  18  motor  impulses  per  second 
from  the  motor  cells  in  the  cord.  Later  ob- 
servers have  found  a  lower  rate.  The  exact  fre- 
quency is  relatively  unimportant  in  comparison 
with  the  main  fact  that  the  motor  cells  have 
a  certain  optimum  rate  of  discharge. 

Neither  direct  nor  indirect  stimulation  with 
currents  of  very  high  frequency  (about  2500  or 
more  per  second)  causes  tetanus  ;  at  the  most, 
these  currents  cause  only  a  twitch  at  the  begin- 
ning of  stimulation. 

Relation  of  Shortening  in  a  Single  Contraction  to 
Shortening  in  Tetanus.  —  1.  Kecord  side  by  side 
the  contractions  of  a  muscle  unloaded  except  by 
the  muscle  lever.  Stimulate  with  a  single  max- 
imal induction  current;  stimulate  with  a  brief 
tetanizing  current. 

The  shortening  of  the  single  twitch  of  the  mi- 


216   THE  PHYSIOLOGY  OF  MUSCLE  AND  NEKVE 

loaded  muscle  is  as  great  as  the  shortening  in 
tetanus. 

2.  Load  the  muscle  with  ten  grams  and  repeat 
Experiment  1. 

The  shortening  in  tetanus  will  now  be  con- 
siderably greater  than  that  of  the  single  twitch. 

3.  Load  the  muscle  with  ten  grams  but  sup- 
port the  weight  by  the  after-loading  screw,  so 
that  the  weight  cannot  pull  on  the  muscle  until 
the  contraction  begins.  Eecord  one  contraction 
on  a  stationary  drum  in  response  to  a  maximal 
make  induction  current.  Turn  the  drum  one 
millimetre.  Kaise  the  writing  point  of  the  lever 
one  millimetre  by  means  of  the  after-loading 
screw.  Stimulate  the  muscle  with  a  make  in- 
duction current  of  the  same  intensity  as  before. 
Again  turn  the  drum  and  raise  the  point  of  the 
lever  one  millimetre,  and  stimulate  the  muscle 
as  before.  Continue  this  until  the  after-loading 
screw  is  raised  so  high  that  the  muscle  no  longer 
shortens  sufficiently  to  raise  the  lever. 

Obviously  in  this  experiment  the  weight  is  arti- 
ficially supported  during  a  progressively  greater 
portion  of  the  contraction.  It  will  be  found  that 
the  total  shortening  of  the  muscle  loaded  only 
during  the  latter  portion  of  the  contraction  is 
as  great  as  the  shortening  of  a  loaded  muscle  in 
tetanus.     These  experiments   suggested   to   von 


THE    CHANGE   IN    FORM  217 

Frey  an  explanation  of  the  greater  shortening  of 
tetanized  muscle  as  compared  with  the  shorten- 
ing of  the  single  contraction.  The  early  con- 
tractions in  tetanus  may  support  the  load  and 
thus  favor  the  succeeding  contractions  just  as 
the  artificial  support  through  the  earlier  stages 
of  the  single  contraction  increases  the  height  to 
which  the  load  is  lifted  in  the  later  stages. 

It  is  possible,  in  muscles  made  up  of  both 
quickly  and  slowly  contracting  fibres,  that  the 
continued  shortening  of  tetanus  may  be  due  to 
the  contraction  of  different  sets  of  fibres.  As 
the  contraction  of  each  new  group  is  added  to  the 
rest,  the  muscle  shortens  more  and  more.  Griitz- 
ner  points  out  that  the  long-continued  contrac- 
tion of  the  fibres  rich  in  sarcoplasm  may  be 
supposed  to  furnish  the  "support"  recpuired  by 
the  hypothesis  of  von  Frey.  It  is  difficult,  how- 
ever, to  explain  in  this  way  the  tetanus  observed 
in  muscles  composed  almost  wholly  of  quickly 
contracting  fibres.' 

The  Isometric  Method 

Thus  far  we  have  observed  the  development 
of  energy  in  a  muscle  stretched  by  a  small  un- 
varying load.  The  principal  part  of  the  energy 
set  free  in  this  isotonic  process  appears  as  the 
mechanical  energy  of  a  visible  change  in  form ; 


218      THE   PHYSIOLOGY   OF   MUSCLE   AND    NERVE 

a  small  part  of  the  energy  of  the  muscle  is  con- 
verted into  tension.  Pick  has  pointed  out  that 
if  the  muscle  be  made  to  pull  against  a  strong 
spring,  the  change  in  the  length  of  the  muscle 
will  be  very  slight  and  the  greater  portion  of  the 
energy  will  be  converted  into  tension  and  stored 
in  the  spring.  If  the  excursion  of  the  spring  be 
recorded  by  a  writing  lever,  the  curve  will  be 
practically  a  record  of  the  Course  of  transforma- 
tion of  energy  into  tension,  and  will  be  only  to  a 
slight  extent  the  record  of  a  change  in  form. 

In  order  to  determine  the  amount  of  energy 
converted  into  tension  in  the  isometric  contrac- 
tion, it  is  necessary  to  graduate  the  spring  against 
which  the  muscle  pulls. 

Graduation  of  Isometric  Spring.  —  To  the  strong 
spring  of  the  apparatus  shown  in  Fig.  48,  is 
attached  a  vertical  bar  on  which  rests  the  writ- 
ing lever.  To  the  lower  end  of  this  bar  attach 
the  large  scale-pan.  Place  a  long  straw  on 
the  lever.  Bring  the  writing  point  against  the 
smoked  paper  of  a  kymograph.  Turn  the  drum 
once  round  to  record  an  abscissa.  Return  the 
drum  to  its  former  position,  and  place  100  grams 
in  the  scale-pan  attached  to  the  spring.  "When 
the  spring  is  stretched  turn  the  drum  once  round 
to  record  the  bending  under  100  grams'  weight. 
Eestore  the  drum  to  its  former  position,  add  100 


THE   CHANGE    IN"    FORM  219 

grams,  and  make  record  of  the  extension  at  200 
grams.  Continue  the  record  up  to  1000  grams. 
Preserve  the  curve  for  reference  (page  229). 

Isometric  Contraction.  —  Fasten  the  femur  of  a 

gastrocnemius  preparation  in  the  muscle  clamp, 
and  the  Achilles  tendon  to  the  bar  connecting 

the  lever  with  the  spring.  Connect  the  binding 
posts  on  the  lever  and  the  clamp  with  the  secon- 
dary coil  of  the  indnctorium,  arranged  for  single 
maximal  induction  currents.  Remove  the  straw 
from  the  lever  and  bring  the  usual  writing  point 
of  the  lever  (which  is  arranged  for  vertical 
writing),  against  a  freshly  smoked  surface.  Let 
the  drum  revolve  at  a  rapid  speed.  Stimulate 
the  muscle  with  a  maximal  break  current. 

An  isometric  contraction  will  be  recorded. 

Remove  the  bar  between  the  spring  and  the 
writing  lever,  and  attach  the  tendon  to  the  lever 
itself.  Stimulate  the  muscle  with  a  break  induc- 
tion current  of  the  strength  used  before. 

The  usual  isotonic  curve  will  be  written. 
Comparison  of  the  isometric  and  isotonic  curves 
reveals  as  a  rule  in  the  isometric  curve  a  longer 
phase  of  rising  energy  and  a  flattened  summit 
or  plateau.  The  muscle  reaches  its  maximum 
tension  sooner  than  its  maximum  shortening  and 
maintains  the  maximum  tension  longer  than  the 
maximum  shortening. 


220   THE  PHYSIOLOGY  OF  MUSCLE  AND  NERVE 


Contraction  of  Human  Muscle 

Simple  Contraction  or  Twitch.  —  Place  the  mid- 
dle, ring,  and  little  fingers  in  the  support  of  the 
ergograph  (Fig.  50).  Let  the  adjustable  rod  rest 
on  the  index  finger  near  the  distal  end  of  the 
middle  phalanx.  Place  the  point  of  the  rod  in 
the   hole   nearest   the   free   end   of   the   spring. 

Adjust  the  writing 
point  to  write  on 
a  smoked  drum 
revolving  at  mod- 
erate speed.  With 
the  brass  elec- 
trodes covered 
with  wet  cotton 
(page  91),  stimu- 
late the  abductor  indicis  with  a  single  maximal 
break  induction  current.  Compare  the  form  of 
the  curve  thus  obtained  with  the  contraction 
curve  of  the  skeletal  muscle  of  the  frog. 
„  Isometric  Contraction.  —  Place  the  point  of  the 
adjustable  rod  in  the  hole  nearest  the  cast-iron 
support  of  the  spring.  The  movement  of  the 
spring  is  so  much  less  at  this  point  that  almost 
none  of  the  energy  of  the  muscle  will  be  con- 
verted into  mechanical  motion.  Stimulate  the 
muscle  as  before  with  a  maximal  break  induc- 


Fig.  50.  The  ergograph  ;  also  employed 
for  recording  the  isometric  and  isotonic  con- 
tractions of  human  muscle. 


THE  CHANGE   IN    FORM  22] 

tion  current.  Compare  the  isometric  curve  thus 
recorded  with  the  largely  isotonic  curve  pre- 
viously obtained. 

Artificial  Tetanus. — Replace  the  adjustable  rod 
in  its  former  position  (isotonic  arrangement). 
Stimulate  the  abductor  with  the  tetanizing  cur- 
rent  of  the  inductorium.  Compare  the  curve 
with  the  tetanus  of  frog  muscle. 

Natural  Tetanus.  —  1.  Contract  the  abductor 
by  voluntary  impulse.  This  also  gives  a  teta- 
nus curve  (page  212).  When  the  natural  tetanus 
is  prolonged,  it  frequently  is  marked  by  oscil- 
lations having  a  periodicity  of  about  ten  per 
minute. 

2.  Place  the  adjustable  rod  in  the  hole  nearest 
the  iron  support  (isometric  arrangement).  Stimu- 
late the  muscle  (1)  with  the  tetanizing  current 
of  the  inductorium  ;  (2)  by  voluntary  impulse. 

It  will  be  seen  that  the  energy  set  free  by  the 
natural  stimulus  is  much  greater  than  when  the 
muscle  is  stimulated  artificially. 

Smooth  Muscle 

Spontaneous  Contractions.  —  Make  two  cuts, 
5  mm.  apart,  through  the  frog's  stomach  at 
righl  angles  to  the  long  axis.  Pass  a  bent  hook 
through  the  ring  (/.  e.  through  the  cavity  of  the 
stomach),  and   fasten   the    hook    in    the    muscle 


222      THE    PHYSIOLOGY   OF   MUSCLE    AND   NERVE 

clamp.  Pass  a  second  hook  around  the  lower 
margin  of  the  ring  and  attach  it  by  means  of  a 
fine  copper  wire  to  the  straw  of  the  heart  lever 
(Fig.  42).  Contraction  of  the  circular  fibres  can 
thus  be  made  visible.  Bring  the  writing  point 
against  a  drum  revolving  about  once  an  hour. 
Wrap  filter  paper  saturated  with  normal  saline 
solution  about  the  muscle  ring.  Keep  this 
thoroughly  moist.  Proceed  to  the  remaining  ex- 
periments, observing  the  stomach  preparation 
from  time  to  time. 

Spontaneous  rhythmic  contractions  will  appear. 
Note  the  changes  in  tonus. 

Simple  Contraction.  —  Prepare  a  second  ring 
of  frog's  stomach  in  the  manner  described  in 
the  preceding  experiment.  Attach  the  lower 
margin  of  the  ring  to  the  muscle  lever  by  means 
of  a  fine  copper  wire.  Carry  the  end  of  the 
copper  wire  to  the  binding  post  on  the  muscle 
lever.  Connect  this  post  and  the  post  on  the 
muscle  clamp  with  a  dry  cell,  interposing  a  sim- 
ple key.  Place  the  electromagnetic  signal  in  the 
primary  circuit.  Bring  the  writing  points  of  the 
muscle  lever  and  the  signal  against  a  smoked 
drum  in  the  same  vertical  line.  Arrange  a  tun- 
ing fork  with  its  writing  point  in  this  line  also. 
Let  the  drum  move  at  rapid  speed.  Set  the 
tuning  fork  vibrating.     Stimulate  the  muscle  by 


THE   CHANGE   IN   FORM  223 

making  and  breaking  the  galvanic  current  once, 
not  oftener. 

Compare  the  duration  of  the  latent  period  with 
that  of  skeletal  muscle.     Compare   the  form  of 

the  contraction  curve  with  that  of  skeletal 
muscle. 

Tetanus.  Determine  how  frequent  the  stimuli 
must  be  in  order  that  the  separate  contractions 
may  be  fused  into  a  smooth  curve. 

Usually  the  muscle  after  contracting  loses  its 
irritability  for  several  minutes.  If  this  occur, 
the  ring  may  be  laid  aside,  covered  with  filter 
paper  saturated  with  normal  saline  solution. 
Excellent  curves  are  often  obtained  from  muscle 
preserved  in  this  way  for  half  an  hour  or  more. 

The  Work  Done 

Influence  of  Load  on  Work  done.  —  111  the  trac- 
ings obtained  in  the  experiments  on  page  205 
with  loads  of  10  grams  and  upwards  measure 
the  distance  from  the  summit  of  each  curve  to 
the  abscissa.  Calculate  the  gram-millimetres  of 
work  done   at    10,   30,  50,    70,    and    <>0    grams, 

ivh 
usiiiL!'  the  formula  W=- —  in  which  J/' is  work 
°  .  m 

done,  in   grain-millimetres;  w,  the  weighl   lifted 

in  grains,  —  i.  e.  the  weight  of  the  scale-pan  and 

lever  (about  12  grams)  plus  the  weighl    put   into 


224      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

the  scale-pan  (the  weight  of  the  muscle  itself 
may  he  neglected) ;  h,  the  height,  in  millimetres, 
to  which  the  load  is  lifted  ;  m,  the  magnification 
of  the  lever. 

Write  the  results  on  the  smoked  paper. 

Note  that  within  wide  limits  an  increase  in  the 
load  increases  the  work  done  by  the  muscle. 

Absolute  Force  of  Muscle.  —  Secure  the  femur 
of  a  gastrocnemius  muscle  preparation  in  a  mus- 
cle clamp  and  fasten  the  tendon  to  the  rigid 
muscle  lever.  After-load  the  muscle  until  it 
just  fails  to  lift  the  load  when  stimulated  with 
tetanizing  induction  currents. 

The  load  which  neither  extends  a  contracting 
muscle  nor  allows  it  to  shorten  is  a  measure  of 
the  "  absolute  force  "  of  the  muscle. 

Total  Work  done  ;  the  "Work  Adder.  —  Attach  a 
scale-pan  to  the  cord  that  passes  over  the  pulley 
on  the  axle  of  the  work  adder  (Fig.  51).  Clamp 
the  work  adder  to  the  wooden  stand  in  such  a 
way  that  the  scale-pan  hangs  free  of  the  table. 
Fasten  the  tendon  of  the  gastrocnemius  muscle 
preparation  to  the  lever  at  a  distance  from  the 
axis  of  the  pulley  equal  to  the  radius  of  the 
pulley.  Connect  the  binding  post  on  the  work 
adder  and  that  on  the  muscle  clamp  with  the 
secondary  coil  of  an  inductorium  arranged  for 
single    maximal  induction    currents.     Move  the 


THE   CHANGE   IN   FORM  225 

sliding  weight  on  the  lever  to  such  a  point  that 
this  weight  and  that  of  the  lever  itself  will  to- 
gether suffice  to  extend  the  muscle  to  its  original 
length  after  the  contraction  of  the  muscle  in 
response  to  a  single   induction   current.     Bring 


Fig.  51.    The  work  adder ;  (the  wheel  is  of  hard  wood). 

the  writing  point  of  the  lever  against  a  drum 
arranged  to  revolve  very  slowly.  Measure  the 
distance  of  the  pulley  weight  from  the  level  of 
the  axis  of  the  pulley.  The  muscle  now  is 
loaded  with  the  lever  (approximately  20  grams) 
and   after-loaded   with    the   pulley   weight    (50 

15 


226      THE   PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

grams),  70  grams  in  all.  Stimulate  the  muscle 
with  induction  currents  at  intervals  of  one  sec- 
ond until  the  fatigued  muscle  ceases  to  con- 
tract. (Stimulation  may  be  made  by  opening 
and  closing  a  simple  key  in  the  primary  cir- 
cuit in  unison  with  the  beat  of  a  metronome.) 

Measure  the  height  in  millimetres  to  which 
the  pulley  weight  has  been  lifted.  Multiply  this 
height  by  the  sum  of  the  pulley  weight  plus  the 
weight  of  the  lever.  The  product  is  the  total 
work  done  in  gram-millimetres. 

Total  Work  done  estimated  by  Muscle  Curve.  — 
The  total  work  done  by  the  muscle  may  also  be 
estimated  by  measuring  in  millimetres  the  height 
of  each  successive  contraction  recorded  on  the 
smoked  paper,  adding  the  several  heights  together, 
dividing  the  sum  by  the  number  of  times  the 
distance  from  the  fulcrum  of  the  recording  lever 
to  the  point  of  attachment  of  the  muscle  is  con- 
tained in  the  distance  from  the  fulcrum  to  the 
writing  point,  and  multiplying  this  quotient  by 
the  sum  of  the  pulley  weight  plus  the  weight  of 
the  lever. 

In  tetanus  no  weight  is  raised  and  no  visible 
mechanical  work  is  performed.  That  internal 
work  is  performed  is  shown  by  the  rise  in 
temperature. 

Time    Relations  of    Developing    Energy.  —  The 


THE   CHANGE   IN    FOBM  227 

simple  muscle  curve  is  a  graphic  record  of  the 
mechanical  energy  set  free  by  the  muscle  in  lift- 
ing a  certain  load.  It  is  desirable  to  measure  the 
maximum  energy  that  the  muscle  can  set  free  at 
each  moment  from  the  beginning  of  contraction 
to  the  poiut  at  which  the  greatest  shortening  is 
reached. 

Place  the  electromagnetic  signal  in  the  primary 
circuit  of  an  inductorium  arranged  for  maximal 
make  induction  currents.  Arrange  a  tuning  fork 
to  write  on  a  smoked  drum  beneath  the  line 
drawn  by  the  writing  point  of  the  signal.  Fasten 
the  femur  of  a  gastrocnemius  muscle  in  the 
muscle  clamp  and  attach  the  tendon  to  the  rigid 
muscle  lever.  Place  the  three  writing  points  in 
the  same  vertical  line.  Connect  the  binding  posts 
on  the  muscle  clamp  and  the  lever  with  the  posts 
of  the  secondary  coil  of  the  inductorium.  "  After- 
load  "  the  muscle  with  50  grams.  Set  the  tuning 
fork  vibrating.  Spin  the  drum.  Stimulate  the 
muscle  with  a  single  maximal  make  induction 
current. 

The  muscle  will  not  shorten  until  the  energy 
set  free  is  sufficient  to  lift  a  load  of  50  grams. 
Turn  the  drum  until  the  writing  point  of  the 
signal  rests  in  the  line  made  by  the  signal  when 
the  muscle  was  stimulated.  Let  the  drum  be 
stationary.     Set  the  tuning  fork  vibrating.     Its 


228      THE   PHYSIOLOGY  OE   MUSCLE  AND   NERVE 

writing  point  will  mark  a  line  synchronous  with 
that  drawn  by  the  signal  during  the  experiment. 
Eevolve  the  drum  a  little  farther,  until  the 
writing  point  of  the  muscle  lever  reaches  the 
point  at  which  contraction  began.  Set  the 
tuning  fork  vibrating  again.  Its  writing  point 
will  mark  a  line  synchronous  with  the  beginning 
of  contraction.  The  number  of  vibrations  in  the 
tuning  fork  curve  between  the  two  points  just 
recorded  is  the  interval  between  the  stimulation 
of  the  muscle  and  the  point  at  which  the  energy 
set  free  was  sufficient  to  move  a  load  of  50 
grams.     Note  this  interval. 

After-load  the  muscle  with  100,  150,  200,  250, 
and  300  grams,  and  repeat  the  above  experiment 
after  each  addition  of  50  grams. 

On  coordinate  paper  set  down  as  ordinates 
the  several  loads  employed  and  along  the  abscissa 
the  time  intervals  in  hundredths  of  a  second. 
Place  a  dot  at  the  junction  of  the  50-gram  line 
with  the  perpendicular  cutting  the  abscissa  at  the 
figure  indicating  the  interval  observed  between 
stimulation  and  the  moment  when  the  energy 
developed  sufficed  to  raise  the  load.  Eepeat  this 
with  other  loads.  Join  the  dots.  The  resulting 
line  is  a  curve  showing  the  absolute  force  of  the 
muscle  at  successive  intervals  from  the  beginning 
to  the  end  of  the  phase  of  rising  energy. 


THE   CHANGE   IN    FOBM  229 

Record  with  this  same  muscle  an  isometric 
contraction  (page  219).  With  the  aid  of  the 
graduation  scale  of  the  isometric  spring  ascer- 
tain the  maximum  tension  developed  in  the 
isometric  contraction.  Compare  this  result  with 
that  secured  in  the  experiment  just  concluded 
on  the  time  relations  of  developing  energy. 

Elasticity  and  Extensibility 

Elasticity  and  Extensibility  of  a  Metal  Spring.  — 
Clamp  the  ergograph  (Tig.  50)  to  the  table  in 
such  a  way  that  the  writing  point  of  the  ergo- 
graph spring  shall  rest  against  a  smoked  drum. 
Attach  a  scale-pan  to  the  spring  near  the  free 
end.  Turn  the  drum  once  round  by  hand,  thus 
describing  an  abscissa  on  the  smoked  paper. 
With  the  forceps  place  2  ten-gram  weights  very 
carefully  on  the  scale-pan. 

The  spring  extends.  Turn  the  drum  2  mm. 
and  add  another  20  grams  to  the  scale-pan. 

A  further  extension  of  the  spring  will  be 
recorded. 

Turn  the  drum  2  mm.  again.  Continue  to 
record  the  extension  of  the  spring  after  each 
addition  of  20  grams  until  a  load  of  200  grams 
has  been  reached. 

It  will  be  found  that  the  extension  curve  is  a 


230      THE  PHYSIOLOGY   OF   MUSCLE   AND   NERVE 

straight  line.  The  extension  is  directly  propor- 
tional to  the  weights  employed. 

Kemove  the  weights  20  grams  at  a  time,  turn- 
ing the  drum  2  mm.  after  each  lightening. 

The  spring  will  return  to  its  former  length. 
Its  elasticity  (within  the  limits  of  extension  here 
used)  is  perfect. 

Of  a  Rubber  Band.  —  Place  the  muscle  clamp 
in  the  stand  of  the  rigid  muscle  lever  (Fig.  48). 
Secure  a  rubber  band  in  the  jaws  of  the  clamp 
and  fasten  the  other  end  of  the  band  to  the 
muscle  lever.  Kepeat  the  preceding  experi- 
ment, using  10-gram  loads  instead  of  20-gram 
loads. 

The  extension  curve  will  again  be  a  straight 
line.  The  return  to  the  original  length  will  not 
be  complete.  The  elasticity  of  the  rubber  band 
is  not  perfect.  An  "extension  remainder"  is 
present.  After  a  considerable  time  the  exten- 
sion remainder  will  disappear  and  the  band  will 
return  to  its  former  length,  provided  the  exten- 
sion was  not  too  violent  nor  too  long-continued. 

Of  Skeletal  Muscle.  —  Isolate  in  both  limbs  the 
mass  of  long,  parallel-fibred  muscles  extending 
along  the  inner  side  of  the  thigh  from  the  pelvis 
to  the  tibia.  Separate  from  the  remainder  of  the 
pelvis  the  portion  to  which  the  muscles  of  both 
sides  are  attached.     Eemove  the  muscles  of  both 


THE   CHANGE    IN    KoRM  231 

sides  together  with  the  part  of  the  tibia  and  the 
pelvis  in  which  they  are  inserted.  The  muscles 
of  the  two  sides  thus  form  practically  one  long 
muscle  held  together  in  the  middle  by  the  small 
piece  of  bone  into  which  they  both  are  inserted 
(Fick's  preparation,  Fig.  48). 

Repeat  the  preceding  experiment,  using  this 
preparation  in  place  of  the  rubber  band. 

The  extension  curve  is  no  longer  a  straight 
line,  but  approximately  a  parabola.  In  organic 
bodies,  the  increase  in  length  is  not  proportional 
to  the  extending  weights,  but  grows  smaller  as 
the  weight  increases. 

A  perfectly  fresh  muscle  weighted  lightly  (e.  g. 
10  grams)  usually  returns  to  its  original  length 
when  the  extending  weight  is  removed.  With 
larger  weights,  the  return  is  not  at  first  com- 
plete :  an  extension  remainder  is  observed,  and 
the  original  length  is  reached  only  after  a  con- 
siderable time. 

Extensibility  increased  in  Tetanus.  —  With  the 
gastrocnemius  muscle  (unloaded  except  by  the 
writing  lever  and  scale-pan)  draw  an  abscissa  (1) 
with  the  muscle  at  rest;  (2)  with  the  muscle 
tetanized.  These  abscissa?  record  the  length  of 
the  practically  unloaded  muscle  in  the  resting 
and  the  active  states.  Place  10  grams  in  the 
scale-pan  and   again  record   the   length    of    the 


232      THE  PHYSIOLOGY  OF   MUSCLE  AND   NEKVE 

muscle  (1)  at  rest ;  (2)  tetanized.    Make  similar 
records  for  each  10  grams  up  to  100. 

It  will  be  found  that  the  extension  curve  falls 
more  rapidly  in  the  active  than  in  the  rest- 
ing muscle;  the  extensibility  is  increased  in 
tetanus. 

Fatigue 

Skeletal  Muscle  of  Frog.  —  1.  Let  a  gastro- 
cnemius muscle  loaded  with  50  grams  write  its 
contractions  on  a  very  slowly  moving  drum. 
Connect  the  secondary  coil  with  the  binding 
posts  on  the  muscle  clamp  and  the  muscle  lever. 
Stimulate  the  muscle  once  in  two  seconds  with  a 
maximal  induction  current,  using  make  and  break 
currents  alternately.  The  correct  interval  may  be 
obtained  by  listening  to  the  beat  of  a  metronome. 
Continue  to  record  the  contractions  until  the 
muscle  will  no  longer  shorten  when  stimulated 
(exhaustion). 

State  the  characteristic  features  of  the  fatigue 
curve. 

2.  With  a  fresh  muscle  repeat  the  stimulation 
every  two  seconds  until  the  height  of  contraction 
has  diminished  about  one  half.  Now  record  the 
duration  of  the  latent  period,  phase  of  rising 
energy,  and  phase  of  sinking  energy  (page  197) 
on  a  rapidly  moving  drum. 


THE    CHANGE   IN   FORM  233 

Note  the  absolute  and  relative  duration  of 
these  periods  as  compared  with  those  of  muscle 
not  fatigued. 

3.  Stimulate  a  sartorius  from  the  same  frog 
continuously  with  tetanizing  currents  and  record 
the  tetanus  curve. 

State  the  differences  between  the  fatigue  curve 
thus  secured  and  the  curve  obtained  by  less  fre- 
quent stimulation. 

Attention  has  already  been  called  to  the  dif- 
ferences which  depend  on  the  relative  proportion 
of  red  and  clear  fibres  (page  199).  The  latter 
are  more  easily  fatigued. 

Human  Skeletal  Muscle.  —  1.  Arrange  the  ergO- 
graph  to  record  the  contractions  of  the  abductor 
indicis,  as  directed  on  page  220.  Place  the  point 
of  the  adjustable  rod  in  the  hole  nearest  the  free 
end  of  the  spring. 

Prepare  also  the  large  and  small  brass  elec- 
trodes for  artificial  stimulation  of  the  muscle  and 
place  them  in  position. 

Bring  the  writing  point  against  a  very  slowly 
moving  drum.  Contract  the  muscle  voluntarily 
every  two  seconds,  keeping  time  with  the  beat  of 
a  metronome,  until  two  hundred  contractions 
have  been  made. 

Now  stimulate  artificially  every  two  sec- 
onds, using  maximal  make  and  break  currents 


234      THE   PHYSIOLOGY   OF   MUSCLE    AND   NEBVE 

alternately,  until  two  hundred  contractions  have 
been  made. 

State  the  characteristics  of  the  two  fatigue 
curves,  and  compare  the  curves  with  those 
obtained  from  frog's  skeletal  muscle. 

2.  From  a  fresh  subject  obtain  a  fatigue  curve 
by  artificial  stimulation  of  the  abductor  indicis, 
using  maximal  make  and  break  induction  cur- 
rents alternately  every  two  seconds,  as  directed 
in  the  preceding  experiment.  When  the  muscle 
has  been  stimulated  two  hundred  times,  contract 
it  voluntarily  every  two  seconds  until  two  hun- 
dred contractions  have  been  made. 

Compare  the  curves  with  those  obtained  in 
Experiment  1. 

Explain  these  paradoxes. 

It  has  been  pointed  out  on  page  223  that 
smooth  muscle  loses  its  irritability  much  more 
rapidly  than  striated  muscle. 

Apparatus 

Normal  saline.-  Bowl.  Towel.  Pipette.  Glass  plate. 
Volume  tube.  Bunsen  burner.  Inductorium.  Two  dry- 
cells.  Wires.  Muscle  clamp.  Fine  copper  wire.  One 
hundred  ten-gram  weights.  Muscle  lever.  Electromag- 
netic signal.  Kymograph.  Tuning  fork.  Cork  clamp. 
Four  needle  electrodes.  Pole-changer.  Pin.  Cork.  Two 
stands  with  clamps.  Ten  one-gram  weights.  Muscle- 
warmer.      Split  shot.     Ice.      One   per  cent   solution  of 


THE   CHANGE  IN    FOK.M  235 

veratrine  acetate.  Wheel-interrupter.  Vibrating  reed, 
Straw  30  cm.  Long  with  platinum  contact.  Mercury  cup. 
Rigid  muscle  lever.  Spring  ergograph  with  rod.  Hand 
clamp.  Ergograph  clamp.  Large  weight  pan.  Cotton. 
Two  bent  hooks.  Heart-holder.  Filter  paper.  Simple 
key.  Work  adder.  Co-ordinate  paper.  Rubber  band. 
Metronome. 


PART   II 
THE   CIRCULATION   OF   THE   BLOOD 


PART   II 
THE  CIRCULATION   OF    THE   BLOOD 

IX 

THE  MECHANICS  OF  THE  CIRCULATION 

The  spaces  between  the  cells  of  which  the  body 
is  composed  are  filled  with  a  liquid  called  the 
lymph,  from  which  the  cells  take  their  food  and 
into  which  they  pour  their  waste.  The  materials 
and  the  products  of  metabolism  diffuse  from 
lymph  to  cell  and  from  cell  to  lymph.  In 
animals  in  which  the  division  of  labor  has 
produced  separate  organs  for  digestion,  excre- 
tion, and  the  like,  the  lymph  serves  as  a  medium 
of  exchange.  For  this  purpose  the  relatively 
slow  processes  of  diffusion  are  not  sufficient. 
Food  must  be  more  rapidly  brought  and  waste 
more  rapidly  removed.  A  circulation  must  be 
provided.  There  are  many  ways  in  which  the 
necessary  circulation  is  secured.  In  Cyclops  a 
flow  is  caused  by  movements  of  the  alimentary 


240  THE   CIRCULATION   OF   THE   BLOOD 

canal.  In  Daphnia,  the  lymph  enters  a  hollow 
muscle  and  is  then  expelled.  In  the  higher 
animals  the  provision  for  rapid  exchange  is  two- 
fold. The  intercellular  spaces  are  traversed  by  a 
countless  number  of  tubes  of  capillary  size,  the 
walls  of  which  are  so  thin  that  substances  in 
solution  pass  through  them  with  great  ease. 
These  capillaries  are  the  ultimate  branches  of 
a  single  tube,  and,  after  fulfilling  their  function, 
the  capillaries  unite  into  a  single  tube  again.  A 
closed  system  is  thus  formed.  This  system  is 
filled  with  a  modified  lymph  called  the  blood, 
which  is  kept  in  constant  circulation.  Thus  the 
lymph  in  the  intervascular  spaces  is  in  intimate 
contact  with  a  continually  changing  liquid. 
Further  provision  for  rapid  exchange  is  found 
in  the  circulation  of  the  lymph  itself.  The 
spaces  between  the  cells  are  drained  by  channels 
which  gradually  become  definite  tubes,  the  lym- 
phatics, and  these  finally  join  to  form  two  ducts 
which  empty  into  the  blood  vessels. 

The  unbranched  portion  of  the  vascular  tube 
is  dilated  into  a  cavity  with  thickened  muscular 
walls  termed  the  ventricle  of  the  heart.  The 
ventricle  contracts  rhythmically.  Each  contrac- 
tion raises  the  pressure  in  the  ventricle  until  it  is 
higher  than  the  pressure  in  the  remaining  blood 
vessels.     The  blood  in  the  ventricle  is  thereby 


THE    MECHANICS    OF   THE   CIRCULATION      241 

forced  into  the  blood  vessels  against  the  resist- 
ance of  friction.  The  high  pressure  in  the  ven- 
tricle during  contraction  is  transmitted  into  the 
blood  vessels  and  through  them.  At  each  cross- 
section  of  the  vascular  system  some  of  the  pres- 
sure is  lost  in  overcoming  resistance  ;  hence  the 
pressure  gradually  falls.  The  blood  flows  from 
the  area  of  higher  pressure,  near  the  ventricle,  to 
the  area  of  lower  pressure.  Thus  the  contrac- 
tions of  the  ventricle  establish  a  difference  of 
pressure  in  the  blood  vessels,  which  causes  a 
movement  of  the  contained  liquid. 

At  the  two  points  at  which  the  vascular 
tube  joins  the  ventricle  membranous  valves  are 
placed.  One  of  these  valves  opens  into  the 
ventricle.  It  is  an  inflow  valve.  The  inflow 
valve  closes  when  the  ventricle  contracts.  Con- 
secpiently  the  contractions  cannot  drive  the 
blood  through  this  orifice.  The  ventricle  can 
drive  the  blood  only  through  the  remaining 
orifice.  Thus  the  ventricle  becomes  a  pump 
and  its  contractions  move  the  blood  always 
in  one  direction.  The  vessels  by  which  the 
blood  is  carried  from  the  ventricle  to  the  cap- 
illaries are  called  arteries ;  those  which  bring 
the  blood  from  the  capillaries  back  to  the  ven- 
tricle are  called  veins.  Adjoining  the  ventricle 
the    great    veins    meet    in    a    common    enlarge- 

16 


242  THE    CIRCULATION    OF   THE    BLOOD 

ment  called  the  auricle.  It  is  at  the  junction  of 
the  auricle  with  the  ventricle  that  the  inflow 
valve  is  placed. 

The  outflow  valve  is  placed  at  that  orifice  of 
the  ventricle  which  opens  into  the  arteries. 
When  the  ventricle,  having  by  its  contraction 
raised  the  pressure  in  the  arteries,  begins  to 
relax,  the  pressure  within  its  cavity  becomes  less 
than  that  in  the  arteries.  The  outflow  valve 
then  shuts.  Otherwise  the  arteries  would  be 
placed  in  direct  communication  with  an  area  of 
low  pressure  and  the  relaxation  of  the  ventricle 
would  undo  in  part  the  work  of  the  contraction, 
the  purpose  of  which  was  the  creation  of  a  pres- 
sure in  the  arteries  great  enough  to  force  the 
blood  through  all  the  blood  vessels. 

It  is  obvious  from  these  general  considerations 
that  the  problems  of  the  circulation  are  in  the 
first  instance  those  joresented  by  any  system  of 
closed  tubes  through  which  liquid  is  driven  by  a 
pump. 

The  Artificial  Scheme 

The  artificial  scheme  (Fig.  52)  to  illustrate  the 
mechanics  of  the  circulation  in  the  highest  verte- 
brates consists  of  a  pump,  a  system  of  elastic 
tubes,  and  a  peripheral  resistance.  The  inlet  and 
the  outlet  tubes  of  the  pump  are  provided  with 


THE   MECHANICS   OF   THE   CIRCULATION       243 

valves  that  permit  a  ilow  in  one  direction  only. 
Between  the  pump  and  the  outlet  valve  is  a  side 
branch  leading  to  a  membrane  manometer  which 
records  the  changes  in  the  pressure  within  the 
pump  (the  loss  in  conveying  the  pressure  through 
short  wide  tubes  filled  with  water  may  be  neg- 


Fig.  52.     Tlie  artificial  scheme  of  the  circulation.1 

lected).  The  peripheral  resistance  consists  chiefly 
in  a  great  number  of  minute  channels  formed  by 
the  interstices  between  shot  in  a  glass  tube.  To 
this  must  be  added  the  slighter  resistance  due  to 
friction  in  the  tubes.  A  mercury  manometer  is 
placed  between  the  pump  and  the  capillary  re- 
sistance, and  a  second  manometer  on  the  distal 


1  The  rubber  tube  on  the  distal  limb  of  the  arterial  manome- 
ter is  filled  loosely  with  cotton  to  prevent  the  mercury  being 
driven  out  by  the  undue  compression  of  the  bulb. 


244  THE   CIRCULATION   OF   THE   BLOOD 

side  of  the  capillary  resistance.  A  side  branch 
which  opens  between  the  capillary  resistance  and 
the  pump  permits  the  discharge  from  the- pump 
to  flow  out  of  the  system  without  passing  through 
the  capillary  resistance. 

In  this  system  the  pump  represents  the  left 
ventricle ;  the  valves  in  the  inlet  and  outlet 
tubes  the  mitral  and  aortic  valves,  respectively ; 
the  resistance  of  the  shot  the  resistance  of  the 
small  arteries  and  capillaries.  The  tubes  be- 
tween the  pump  and  the  resistance  are  the  arte- 
ries ;  those  on  the  distal  side  of  the  resistance 
are  the  veins.  The  side  branch  substitutes  a 
wide  channel  for  the  narrow  ones  and  thus  is 
equivalent  to  a  dilatation  of  the  vessels.  The 
mercury  manometer  on  the  proximal  side  of  the 
resistance  measures  the  arterial  pressure  ;  that  on 
the  distal  side  the  venous  pressure.  The  mem- 
brane manometer,  inserted  on  the  ventricular 
side  of  the  aortic  valve,  records  the  time-relations 
of  the  intraventricular  pressure  curve. 

The  Conversion  of  the  Intermittent  into  a 
Continuous  Flow 

When  a  pump  forces  water  or  any  other 
incompressible  fluid  through  tubes  with  rigid 
walls,  the  inflow  and  outflow  are  equal  and  in  the 


THE    MECHANICS   OF   THE   CIRCULATION      245 

same  time.  The  outflow  ceases  the  instant  the 
inflow  ceases.  The  same  is  true  in  a  system  of 
elastic  tubes  so  short  and  wide  that  friction  be- 
tween the  liquid  and  the  walls  causes  practically 
no  resistance  to  the  now.  Here  the  quantity 
received  from  the  pump  can  still  escape  from  the 
distal  end  of  the  system  during  the  stroke  of  the 
pump.  "When  the  resistance  is  increased  by 
narrowing  the  tubes,  or  by  increasing  their 
length,  or  in  both  these  ways,  not  all  the  liquid 
received  from  the  pump  can  pass  by  the  resist- 
ance during  the  stroke  of  the  pump,  —  the  re- 
mainder must  pass  during  the  interval  between 
one  stroke  and  the  next.  The  portion  which 
cannot  pass  during  the  stroke  finds  room  be- 
tween the  pump  and  the  resistance  in  the  dilata- 
tion of  the  containing  vessels.  To  effect  the 
dilatation  the  force  or  pressure  transmitted  from 
the  pump  presses  out  the  vessel  walls  until  this 
pressure  is  held  in  equilibrium  by  the  elastic  re- 
action of  the  walls.  As  the  pressure  from  the 
pump  wanes,  the  energy  stored  by  it  in  the  ten- 
sion of  the  vessel  walls  is  reconverted  into 
mechanical  motion,  and  the  walls  return  towards 
their  original  position,  driving  the  liquid  out  of 
the  tube  past  the  resistance. 

1.  Open  the  side  branch  by   unscrewing    the 
pressure-clip.     See  that  the  tubes  are  well  rilled 


246  THE   CIRCULATION   OF   THE   BLOOD 

with  water.     Make  a  single  brief  gentle  pressure 
on  the  bulb. 

Note  (1)  that  practically  all  the  liquid  driven 
out  by  the  stroke  escapes  through  the  side 
branch,  in  which  the  resistance  is  low,  rather 
than  through  the  high  capillary  resistance. 
(2)  Only  a  portion  of  the  liquid  escapes  during 
the  stroke.  (3),,  The  portion  which  cannot 
escape  by  the  resistance  during  the  stroke  finds 
space  in  a  very  evident  dilatation  of  the  tubes 
nearer  the  pump,  i.e.  between  the  pump  and  the 
principal  resistance.  (4)  The  membrane  man- 
ometer shows  a  sudden  rise  and  fall  indicating 
a  sudden  rise  and  fall  in  the  intraventricular 
pressure.  (5)  Close  observation  shows  that  on 
the  stroke  of  the  pump  the  tubing  just  distal  to 
the  aortic  valve  begins  to  expand  sooner  than 
that  farther  away.  Evidently  the  change  of 
pressure  produced  by  the  stroke  of  the  pump  is 
transmitted  from  point  to  point  through  the 
liquid  in  the  tubes.  (6)  The  arterial  manometer 
shows  a  sudden  rise  and  fall.  Observe  that  the 
rise  is  not  synchronous  with  the  stroke  of  the 
pump,  but  begins  an  instant  later.  This  interval 
is  occupied  by  the  transmission  of  the  pressure 
change  from  the  pump  to  the  mercury  column, 
and  in  part  by  the  time  required  to  overcome  the 
inertia  of  position  of  the  mercury.     The  oscilla- 


THE    M  IK  HANK'S    OF   THE    CIRCULATION       247 

tions  of  the  mercury  following  the  primary  rise 
and  fall  are  due  to  inertia.  (7)  Observe  the  action 
of  the  valves  (they  consist  <>f  a  glass  tube,  closed 
at  one  end,  and  pierced  with  a  hole  which  is 
covered  with  a  rubber  flap  tied  on  both  sides  of 
the  hole).  (8)  Place  a  finger  on  the  "aorta" 
near  the  valve  and  note  the  pressure  wave  (pulse) 
as  it  passes  along  the  vessel. 

2.  With  the  side  branch  open  as  in  Experiment 
1,  compress  the  bulb  rhythmically  and  gradually 
increase  the  frequency  of  stroke. 

It  will  be  found  that  at  about  twenty  strokes 
to  the  minute  the  stream  will  be  intermittent. 
As  the  interval  between  the  strokes  is  shortened 
the  liquid  received  from  the  pump  in  any  one 
stroke  cannot  all  escape  by  the  resistance  during 
the  stroke  and  the  succeeding  interval.  The 
next  stroke  comes  before  the  outflow  from  the 
preceding  stroke  is  finished,  and  the  stream  be- 
comes remittent. 

Still  further  increase  the  frequency  of  the 
stroke.  A  rate  will  be  reached  at  which  one- 
half  the  quantity  received  from  the  pump  will 
pass  by  the  resistance  during  the  stroke  of  the 
pump  and  the  remaining  half  will  pass  in  the 
interval  betweeD  that  stroke  and  the  next; 
the  intermittent  will  be  converted  into  a  con- 
tinuous flow. 


248  THE    CIBCULATION    OF   THE   BLOOD 

Observe  that  the  duration  of  the  intervals  is 
greater  than  the  duration  of  the  strokes  of  the 
pump.  Thus  the  time  during  which  the  circula- 
tion is  carried  on  by  the  energy  stored  by  the 
pump  in  the  elastic  walls  of  the  vessel  is  greater 
than  the  time  during  which  it  is  carried  on  by 
the  direct  stroke  of  the  pump. 

Note  that  the  arterial  pressure  remains  low 
even  after  the  stream  becomes  continuous.  An 
increase  in  the  frequency  of  the  beat  has  little 
influence  on  the  blood  pressure  where  the  peri- 
pheral resistance  is  very  slight. 

3.  Close  the  side  branch,  so  that  the  liquid 
must  pass  through  a  high  peripheral  resistance. 
Compress  the  bulb  at  such  a  rate  that  the  outflow 
shall  be  continuous. 

The  frequency  required  to  make  the  flow  con- 
tinuous is  now  much  less  than  when  the  peri- 
pheral resistance  was  low. 

The  Relation  between  Rate  of  Flow  and 

Width  of  Bed 

In  a  frog  slightly  paralyzed  with  curare  destroy 
the  brain  by  pithing,  with  the  least  possible  loss 
of  blood.  Lay  the  frog  back  down  on  the  mes- 
entery board.  Open  the  abdomen  in  the  median 
line.     Draw  the  intestine  over   the  cover  glass- 


TIIF.    MECHANICS   OF   THE   CIRCULATION      249 

upon  the  cork  ring  bo  that  the  mesentery  may 
lie  upon  the  glass  evenly  and  without  stretch- 
ing. The  mesentery  must  lie  kept  <■. >nst;i m  1  \- 
moist   with   normal   saline  solution.      Examine 

thf  blood  vessels  in  the  mesentery  with  No.  3 
Leitz  objective. 

Note  the  swift  flow  in  the  larger  vessels  and 
the  slow  movement  of  the  blood  through  the 
capillaries. 

The  combined  cross-sections  of  the  capillaries  in 
the  body  are  vastly  greater  than  the  cross-section 
of  the  arteries  or  the  veins.  The  total  quantity 
of  blood  passing  in  a  unit  of  time  through  the 
arteries  or  veins  and  the  capillaries  is  the  same. 
If  less  passed  through  the  capillaries  than  through 
the  arteries,  the  capillaries  would  soon  be  gorged 
to  bursting.  If  more,  the  arteries  would  soon  be 
empty.  As  the  quantity  passing  through  the 
capillaries  and  the  arteries  and  veins  in  a  unit  of 
time  must  thus  be  the  same,  it  follows  that  where 
the  combined  cross-section  of  the  channel  or 
"  bed  "  is  small,  the  blood  must  flow  faster  than 
where  the  cross-section  is  large.  A  river  rushes 
rapidly  through  a  gorge,  but  moves  sluggishly 
where  meadow-lands  afford  a  wider  channel. 
Thus  the  blood  flows  with  great  velocity  in  the 
great  arteries,  less  rapidly  in  their  branches,  and 
very  slowly  indeed  in  the  capillaries,  the  com- 


250  THE   CIRCULATION   OF   THE   BLOOD 

bined  width  of  which  is  so  great  compared  to 
that  of  the  arteries.  And  as  the  capillaries  unite 
into  the  smaller  veins,  and  these  into  the  larger 
veins,  the  combined  cross-section  or  bed  becomes 
ever  smaller  and  the  blood  moves  ever  more 
swiftly.  Were  the  slow  passage  of  the  blood  in 
the  capillaries  due  simply  to  friction,  the  blood 
would  move  still  more  slowly  in  the  veins  be- 
cause the  retarding  influence  of  the  friction  in 
the  veins  would  be  added  to  that  of  the  capillaries. 
There  is  an  inverse  relation  between  the  rate  of 
flow  and  the  area  of  bed. 

The  Blood-Pkesstjke 

The  Relation  of  Peripheral  Resistance  to  Blood- 
Pressure.  —  Compress  the  bulb  at  a  rate  that  will 
produce  a  continuous  outflow. 

With  each  successive  stroke  the  portion  of 
liquid  unable  to  pass  the  resistance  during  the 
stroke  and  the  succeeding  interval  is  added  to 
that  left  behind  from  preceding  strokes.  The 
arteries  become  more  and  more  full.  The  arte- 
rial manometer  registers  a  higher  and  higher 
pressure.  At  length  the  pressure  ceases  to  rise. 
The  mercury  remains  at  a  mean  level  broken  by 
a  slight  accession  at  each  stroke.  The  pump 
now  merely  maintains  the  constant  high  arterial 
pressure.     This  pressure  suffices  to  drive  through 


THE   MECHANICS   OF  THE   CIRCULATION      251 

the  resistance  during  each  stroke  and  the  suc- 
ceeding interval  all  the  liquid  received  from  the 
pump  during  the  stroke. 

The  venous  pressure  remains  very  low.  The 
capillary  resistance  (to  which  must  especially  be 
added  the  resistance  of  the  smallest  arteries) 
almost  entirely  exhausts  the  pressure  in  the 
arteries.  Hence  the  sudden  and  profound  dif- 
ference observed  between  the  arterial  and  the 
venous  pressure.  A  second  arterial  manometer 
placed  near  the  aorta  would  show  that  the 
loss  of  pressure  between  the  ventricle  and  the 
smallest  arteries  is  relatively  slight. 

The  pulse  is  absent  on  the  venous  side  of  the 
resistance. 

The  Curve  of  Arterial  Pressure  in  the  Frog.  — 
Expose  the  heart  of  a  lightly  curarized  frog  by 
the  method  given  on  page  75.  Provide  a  fine 
cannula  with  a  short  piece  of  rubber  tubing. 
Fill  cannula  and  tube  with  one  per  cent  sodic  car- 
bonate solution,  and  close  the  end  of  the  tube  with 
a  small  glass  rod.  Tie  a  ligature  about  one  aorta 
as  far  as  possible  from  the  junction  of  the  two 
aortas.  Knot  the  ends  of  the  ligature  together. 
Pass  a  second  ligature  beneath  the  same  aorta,  but 
do  not  tie  it.  Lift  the  vessel  by  the  second 
ligature  so  that  the  vessel  is  constricted  by  lying 
across  the  thread.      Between  the  two  ligatures 


252 


THE   CIRCULATION   OF  THE   BLOOD 


open  the  aorta  with  sharp  scissors  and  introduce 
the  cannula.  Fasten  the  cannula  in  place  by 
means  of  the  ligature.  Place  the  frog-board  on 
the  wooden  stand  to  bring  the  heart  on  a  level 
slightly  higher  than  the  level  of  the  mercury  in 
the  mercury  manometer  (Fig.  53).  See  that  the 
proximal  limb  of  the  manometer  is  filled  with 
one  per  cent  sodic  carbonate  solution  to  the  ex- 
clusion of  air.  Bring  the 
writing  point  of  the  man- 
ometer against  a  smoked 
drum  and  revolve  the  drum 
once  by  hand  to  record  a 
line  of  atmospheric  pres- 
sure. Close  the  aorta  con- 
taining the  cannula  by 
gentle  pressure  with  a  for- 
ceps the  blades  of  which 
are  covered  with  rubber 
tubing.  Join  the  cannula- 
tube  to  the  manometer,  excluding  air  bubbles. 
Eemove  the  forceps. 

The  mercury  will  fall  in  the  proximal  and  rise 
in  the  distal  limb  until  the  blood-pressure  in  the 
aorta  is  balanced  by  the  column  of  mercury.  With 
each  ventricular  beat,  the  column  rises  a  short 
distance  above  the  mean  level  and  sinks  again. 
Eecord   the   blood-pressure   curve   on   a   very 


53.      The     mercury 
manometer. 


THE   MECHANICS   OP   THE   CIRCULATION       253 

slowly  moving  drum.  To  get  the  actual  pressure 
in  millimetres  of  mercury  multiply  by  two  the 
mean  height  of  the  curve  above  the  atmospheric 
pressure  line. 

The  Effect  on  Blood-Pressure  of  Increasing  the 
Peripheral  Resistance  in  the  Frog. — The  peripheral 
resistance  may  be  increased  by  the  narrowing  of 
the  small  arteries  which  follows  the  stimulation 
of  special  vaso-constrictor  nerve  fibres.  The  vaso- 
constrictor nerves  may  be  stimulated  directly  or 
rerlexly.     The  latter  method  is  chosen  here. 

Expose  the  sciatic  nerve.  Tie  a  ligature  about 
the  nerve  near  the  distal  end  of  the  wound,  and 
sever  the  nerve  on  the  distal  side  of  the  ligature. 
Stimulate  the  central  end  with  a  tetanizing 
current  of  moderate  strength. 

The  afferent  impulses  set  up  by  the  stimula- 
tion proceed  to  the  spinal  cord  and  thence  to  the 
bulb,  where  they  excite  nerve  cells  which  dis- 
charge impulses  that  cause  the  smaller  arteries 
(and  probably  the  veins)  to  constrict.  This 
narrowing  causes  the  arterial  pressure  to  rise. 

Changes  in  the  Stroke  of  the  Pump  ;  Inhibition 
of  the  Ventricle.  —  While  the  arterial  pressure  in 
the  artificial  scheme  is  at  a  good  height  (120  mm. 
Hg)  arrest  the  ventricular  stroke  (the  ventricle 
in  animals  may  be  thus  inhibited  by  stimula- 
tion of  the  vagus  nerve,  page  2S7). 


254  THE    CIRCULATION    OF   THE   BLOOD 

So  soon  as  the  ventricle  ceases  to  beat,  the  less 
distended  arteries  will  empty  themselves  through 
the  peripheral  resistance,  and  the  arterial  man- 
ometer will  show  a  continuous  fall  in  blood- 
pressure. 

Eesume  the  ventricular  beats. 

The  mercury  in  the  arterial  manometer  will 
rise  in  large  leaps,  corresponding  to  the  ease  with 
which  the  early  strokes  of  the  pump  distend  the 
lax  arteries  (the  inertia  of  the  mercury  somewhat 
exaggerates  the  rise  at  each  stroke).  As  the 
blood-pressure  rises,  however,  the  excursion  of 
the  mercury  for  each  ventricular  stroke  becomes 
less  and  less,  corresponding  to  the  smaller  and 
smaller  difference  between  the  pressure  in  the 
arteries  and  the  maximum  pressure  within  the 
ventricle,  until  at  length  equilibrium  is  restored 
between  the  peripheral  resistance  and  the  force 
and  frequency  of  the  ventricular  beat. 

The  Effect  of  Inhibition  of  the  Heart  on  the 
Blood-Pressure  in  the  Prog. —  Arrange  an  induc- 
torium  for  strong  tetanizing  currents.  Insert 
the  electromagnetic  signal  in  the  primary  circuit 
and  bring  its  writing  point  beneath  that  of  the 
manometer.  Eaise  the  heart  gently.  Note  the 
white  "  crescent "  between  the  sinus  venosus  and 
the  right  auricle.  Put  the  points  of  the  elec- 
trodes   on    the    crescent,   and    open   the    short- 


THE    MECHANICS   OF   THE   CIRCULATION      255 

circuiting  key  for  a  moment.     After  one  or  two 
beats  the  heart  will  Btop. 

Observe  the  great  fall  in  blood-pressure. 
Cease  the  stimulation. 

The  mercury  returns  in  leaps  to  its  former 
level. 

The  Heart  as  a  Pump 

The  Opening  and  Closing  of  the  Valves.  —  Secure 
a  high  arterial  pressure  (120  mm.  Hg)  in  the 
artificial  scheme.  Now  greatly  slow  each  ven- 
tricular beat  and  at  once  observe  closely  the 
action  of  the  valves. 

It  will  be  seen  that  the  mitral  valve  closes  as 
soon  as  the  ventricle  begins  to  contract,  but  the 
aortic  valve  does  not  open  until  the  intraventric- 
ular pressure  has  risen  above  that  in  the  aorta. 
Time  is  required  for  this  rise  in  the  pressure  in 
the  ventricle.  During  this  period  both  mitral 
and  aortic  valves  are  closed.  "When  the  ventri- 
cle begins  to  relax,  the  intraventricular  pressure 
speedily  falls  below  that  in  the  aorta,  and  the 
aortic  valve  shuts,  but  the  intraventricular  pres- 
sure normally  must  fall  at  least  100  mm.  Hg 
farther  before  it  shall  be  lower  than  that  in  the 
auricle.  During  this  fall  all  the  heart  valves  are 
again  closed;  the  aortic  valves  are  already  shut, 
and  the  mitral  not  yet  open. 


256 


THE   CIRCULATION   OF   THE   BLOOD 


The  Period  of  Outflow  from  the  Ventricle.  —  Tie 

a  rubber  membrane  over  the  smaller  thistle-tube 
of  the  sphygmograph  (Fig.  54)  and  cement  a  bone 
button  in  the  centre.  Prepare  a  second  receiv- 
ing tambour  in  the  same  way.  Bring  the  writing 
points  of  the  recording  tambours  into  the  same 
vertical  line   against  a  smoked  drum.     Let  the 

drum  revolve  at 
its  fastest  speed. 
Place  the 
button  of  one  re- 
ceiving tambour 
on  the  aorta, 
the  other  on  the 
membrane  of  the 
tube  which  re- 
cords the  intra- 
ventricular 
pressure.  Let 
the  ventricle  pump  with  the  usual  force  and  fre- 
quency. When  the  two  curves  have  been  written, 
stop  the  clock-work  and  turn  back  the  drum  until 
the  point  of  the  lever  recording  the  ventricular 
pressure  lies  at  the  exact  beginning  of  the  upstroke 
in  the  aortic  pulse  curve.  Cause  each  lever  to 
write  an  ordinate  on  the  stationary  drum.  These 
ordinates  will  indicate  synchronous  points  and 
will  mark  the  beginning  of  the  "  outflow  "  period. 


Pig.  54.    The  sphygmograph. 


THE    MECHANICS   OF   THE    CIRCULATION       257 

Now  turn  the  drum  until  the  point  of  the 
aortic  lever  lies  beneath  the  notch  seen  in  the 
clown  stroke  of  the  pulse  curve  (the  dicrotic 
notch,  see  page  274).  Describe  synchronous 
ordinates.  It  is  known  that  the  dicrotic  notch 
in  the  aortic  pulse  curve  corresponds  closely  to 
the  moment  of  closure  of  the  aortic  valves.  It 
marks,  therefore,  the  end  of  the  outflow  period. 
Xote  that  this  point  is  reached  soon  after  the 
ventricle  begins  to  relax.  Thus  the  period  dur- 
ing which  the  intraventricular  pressure  is  higher 
than  the  pressure  in  the  aorta  embraces  part  of 
the  relaxation  as  well  as  part  of  the  contraction 
of  the  ventricle.  It  includes  approximately  the 
highest  third  of  the  intraventricular  pressure 
curve. 

Observe  also  the  considerable  interval  between 
the  beginning  of  ventricular  contraction  and  the 
opening  of  the  aortic  valve,  as  shown  by  the 
upstroke  in  the  pulse  curve  consequent  upon 
the  entrance  of  liquid  into  the  aorta. 

The  Visible  Change  in  Form.  —  Expose  the  heart 
of  a  frog.  Observe  the  great  veins,  the  auricles, 
the  single  ventricle,  the  two  aorta?,  and  the  dila- 
tation, or  bulbus,  by  which  the  aorta?  are  con- 
nected with  the  ventricle.  All  these  parts  except 
the  two  aorta?  are  contracting.  The  veins  con- 
tract first ;  the  auricles  next ;  then  the  ventricle  ,* 

17 


258  THE    CIRCULATION    OF   THE    BLOOD 

last  the  bulbus.   Note  the  pallor  of  the  contracted, 
empty  ventricle. 

Graphic    Record   of    Ventricular   Contraction.  — 

Set  the  heart-holder  (Fig.  42)  across  the  frog- 
board,  liaise  the  heart  gently  with  a  seeker, 
and  pass  the  spoonlike  tongue  of  the  holder 
beneath  the  heart.  Fill  the  spoon  with  normal 
saline  solution.  Eest  the  upright  of  the  straw 
heart-lever  on  the  ventricle,  but  do  not  allow  the 
weight  of  the  lever  to  remain  on  the  heart  when 
it  is  not  recording.  Adjust  the  preparation  so 
that  the  lever  writes  on  a  slow-moving  drum. 
Note  the  characteristics  of  the  curve. 

The  Heakt  Muscle 

All  Contractions  Maximal.  —  Find  the  least 
strength  of  stimulus  that  will  cause  the  ventri- 
cle to  contract.  Increase  the  strength  of  the 
stimulus,  but  do  not  stimulate  oftener  than  once 
in  ten  seconds  (to  avoid  the  staircase  contractions 
described  below). 

The  force  of  ventricular  contraction  will  re- 
main the  same,  notwithstanding  the  increased 
stimulus. 

If  the  heart  responds  at  all  to  a  stimulus,  it 
responds  by  a  maximum  contraction.  There  is 
no  interval  between  the  minimal  and  maximal 
value  (compare  page  138). 


THE    MECHANICS   OF  THE   C1KCULATTON      259 

Staircase  Contractions. —  Find  the  leasl    -tilnu- 

lua  that  will  cause  the  ventricle  to  contract. 
Repeat  this  minima]  stimulus  every  5  seconds, 
recording  the  contractions  on  a  drum  turned 
about  5  nun.  by  hand  after  each  contraction. 

The  contractions  of  the  ventricle  will  be  suc- 
cessively stronger,  so  that  the  apices  of  the  curves 
will  form  an  ascending  line  ("  staircase  ").  The 
form  of  the  staircase  is  always  an  hyperbola. 
Successively  stronger  responses  to  repeated  stim- 
uli of  uniform  strength  can  also  be  obtained 
from  the  curarized  gastrocnemius  of  the  frog, 
perfused  with  blood,  and  from  mammalian  and 
invertebrate  muscles.  The  contraction  appears  to 
increase  the  irritability.  Thus  the  same  stimu- 
lus causes  a  greater  contraction  after  a  brief 
tetanus  than  before.  Rossbach  and  Bohr  have 
observed  this  after-effect  continuing  more  than 
thirty  minutes. 

The  Isolated  Apex ;  Bernstein's  Experiment.  — 
Draw  a  ligature  about  the  ventricle  halfway  be- 
tween base  and  apex  tightly  enough  to  crush  the 
tissues  without  wholly  separating  them.  The 
anatomical  continuity  between  the  two  halves 
of  the  ventricle  will  thereby  be  maintained,  but 
the  physiological  continuity  will  be  lost.  Eelease 
the  ligature. 

The  isolated  "  apex "  as  a  rule  does  not  con- 


260  THE   CIRCULATION   OF   THE   BLOOD 

tract.  The  exceptions  can  probably  be  explained 
as  the  effect  of  a  constant  stimulus  (see  page 
261). 

The  apical  half  of  the  normal  ventricle  con- 
tains no  nerve  cells.  Consequently  its  failure  to 
contract  after  its  separation  from  the  remainder 
of  the  heart  would  indicate  that  the  adult  heart 
muscle  is  incapable  of  spontaneous  rhythmical 
contraction.  It  has  been  shown,  however,  that  the 
"  apex  "  of  the  mammalian  heart  will  beat  after 
its  complete  removal  from  the  remainder  of  the 
heart,  provided  the  circulation  in  the  extirpated 
piece  is  maintained  by  supplying  it  with  blood. 

Rhythmic  Contractility  of  Heart  Muscle. —  Fur- 
ther evidence  of  the  rhythmic  contractility  of 
the  heart  muscle  is  found  in  the  bulbus  arteriosus. 

Place  very  small  pieces  of  the  bulbus  arteri- 
osus in  normal  saline  solution  under  the 
microscope. 

They  will  contract  rhythmically. 

Histological  examination  shows  that  nerve 
cells  seldom  occur  in  the  bulbus.  It  is  scarcely 
credible  that  they  are  present  in  each  of  the  small 
pieces  seen  contracting  under  the  microscope. 

Constant  Stimulus  may  cause  Periodic  Contrac- 
tion. —  In  a  frog  with  ventricular  apex  isolated 
by  Bernstein's  ligature,  compress  one  or  both 
aortte,  thus  raising  the  pressure  in  the  ventricle. 


THE    MECHANICS    OF   THE   CIRCULATION      261 

The  increased  intracardiac  pressure  acts  as  a 
constant  stimulus  to  the  cardiac  muscle  and  the 
hitherto  inactive  apex  begins  to  contract  again. 

Thus  a  constant  stimulus  may  discharge  peri- 
odic contractions  in  a  muscle  habituated  to 
periodic  contractions  (compare  page  105)  ;  the 
galvanic  current  and  chemical  stimuli,  such  as 
delphinin,  are  further  examples  of  constant  stim- 
uli which  call  forth  rhythmic  contractions  of  the 
heart  muscle. 

The  Inactive  Heart  Muscle  still  Irritable.  — Stim- 
ulate the  inactive  "apex  "  mechanically  and  with 
single  induction  shocks. 

The  apex,  though  incapable  of  spontaneous 
rhythmic  contractions,  is  still  irritable,  and  will 
respond  by  a  single  contraction  to  each  stimulus. 

Refractory  Period  ;  Extra-Contraction ;  Compen- 
satory Pause.  —  Put  the  electromagnetic  signal 
in  the  primary  circuit.  Connect  the  binding- 
posts  on  the  heart-holder  to  the  secondary  coil  of 
the  inductorium.  Arrange  the  latter  for  single 
induction  currents.  Place  the  ventricle  on  the 
heart-holder.  Send  maximal  make  and  break 
induction  currents  through  the  ventricle  from 
time  to  time  in  each  phase  of  the  cardiac  cycle. 

Note  that  (1)  the  stimulus  sometimes  calls 
forth  an  extra-contraction ;  (2)  at  other  times 
the  stimulus  causes  no  contraction,  having  fallen 


262  THE    CIRCULATION   OF   THE    BLOOD 

into  the  ventricle  during  the  period  in  which  it 
is  refractory  towards  stimuli;  (3)  the  extra-con- 
traction is  followed  by  a  pause,  called  the  com- 
pensatory pause  because  it  usually  restores  the 
rate  of  beat  to  that  existing  before  the  extra- 
contraction  took  place. 

Using  induction  currents  of  equal  intensity, 
find  the  limits  of  the  refractory  period  and  note 
them  on  the  drum.  Note  also  the  point  in  the 
cardiac  cycle  at  which  the  maximum  extra- 
contraction  can  be  obtained. 

The  Transmission  of  the  Contraction  Wave  in  the 
Ventricle ;  Engelmann's  Incisions.  —  The  action 
current  of  the  heart  is  taken  to  be  an  expression 
of  the  excitation  process,  although  the  nature  of 
the  latter  is  not  yet  understood.  It  has  already 
been  shown  (page  173)  that  the  action  current 
sweeps  rapidly  over  the  ventricle  preceding  the 
contraction.  The  excitation  might  be  propagated 
by  nerves  or  by  muscle  fibres.  The  following 
experiment  affords  some  evidence  that  the 
transmission  is  by  means  of  muscular  tissue. 

Leaving  the  heart  in  situ,  cut  the  ventricle 
into  a  zigzag  strip  by  obliquely  transverse  in- 
cisions beginning  near  the  apex.  The  nerve 
fibres  in  the  ventricle  will  thereby  be  severed 
at  some  part  or  other  of  their  course,  but  muscular 
continuity  will  be  preserved. 


THE    MEOHANII  s   OF  THE   CIRCULATION       263 

The  contraction  wave  will  pass  over  the  entire 
zigzag  strip.  Normally  the  wave  starts  at  the 
base  and  proceeds  to  the  apex,  but  by  artificial 
stimulation  it  can  be  made  to  pass  from  the 
apex  towards  the  base.  A  similar  result  can  be 
secured  with  the  auricle. 

The  Transmission  of  the  Cardiac  Excitation  from 
Auricle  to  Ventricle:  G-askell's  Block.  —  The  con- 
traction wave  can  be  seen  to  begin  normally  in 
the  sinus  and  thence  to  pass  rapidly  over  the 
auricle ;  on  reaching  the  auriculo-ventricular 
junction  there  is  a  distinct  pause  termed  the 
auriculo-ventricular  interval ;  finally,  the  excita- 
tion reaches  the  ventricle,  and  the  contraction 
wave  is  seen  to  traverse  the  ventricular  muscle 
as  noted  above.  The  auriculo-ventricular  inter- 
val may  be  lengthened  by  any  natural  or  arti- 
ficial hindrance  to  the  passage  of  the  excitation 
wave. 

1.  Place  the  screw-clamp  about  the  auriculo- 
ventricular  junction.  Very  cautiously  turn  the 
screw  until  the  cork  edge  makes  a  gentle 
pressure  on  the  cardiac  tissues  at  that  point 

With  careful  work  a  degree  of  pressure  will  be 
reached  that  diminishes  the  conductivity  of  the 
muscle  fibres  joining  the  auricle  and  ventricle  so 
far  as  to  permit  only  every  second  or  every  third 
excitation  to  pass.     The  auricle  will  beat  with- 


264  THE    CIKCULATION    OF    THE    BLOOD 

out  change  of  frequency,  but  the  ventricle  will 
contract  only  when  the  excitation  succeeds  in 
passing  the  block. 

2.  Divide  the  auricles  in  two  •  pieces  con- 
nected by  a  small  bridge  of  auricular  tissue. 
Stimulate  one  piece. 

The  stimulation  of  one  piece  will  be  followed 
immediately  by  the  contraction  of  that  piece, 
and,  after  an  interval,  by  the  contraction  of  the 
other.  The  smaller  the  bridge,  the  longer  the 
interval. 

Gaskell  has  pointed  out  that  a  natural  block 
is  furnished  by  the  small  number  of  the  muscle 
fibres  joining  the  auricle  to  the  ventricle,  and 
that  this  natural  block  explains  the  auriculo- 
ventricular  interval,  i.  e.  the  delay  which  the 
excitation  experiences  in  passing  from  the  auricle 
to  the  ventricle. 

3.  Eepeat  Experiment  1,  but  place  the  screw- 
clamp  across  the  middle  of  the  ventricle. 

The  passage  of  the  excitation  from  one  part  of 
the  ventricle  to  another  will  be  delayed  or  inter- 
rupted by  the  lowering  of  the  conductivity  in 
the  compressed  portion. 

Many  irregularities  in  the  frequency  and  force 
of  the  heart  can  be  explained  by  variation  in  the 
conductivity  of  its  several  parts.  They  can  be 
explained  also  by  variations  in  the  irritability  of 


THE    MECHANICS   OF  THE   CIRCULATION      265 

the  several  parts.  In  the  latter  case,  the  excita- 
tion would  pass  as  usual,  but  its  action  on  any 
part,  for  example  the  ventricle,  would  be  in- 
creased or  diminished  by  changes  in  the  irri- 
tability of  the  cardiac  muscle  in  that  region. 
Engelmann  has  found  that  ventricular  systole 
lowers  the  conductivity  of  the  ventricle  for  a 
time. 

Tonus.  —  Counterpoise  the  muscle  lever  by 
placing  weights  in  the  weight  pan  suspended 
from  the  pulley.  Pass  the  very  fine  copper  wire 
through  the  wall  of  the  auricle  of  the  tortoise 
and  attach  the  wire  to  the  counterpoised  muscle 
lever,  so  that  the  contractions  of  the  auricle  may 
be  recorded.  Let  the  drum  move  so  slowly  that 
the  individual  contractions  will  be  nearly  but  not 
quite  fused. 

Two  sorts  of  contractions  can  be  distinguished, 
(1)  the  usual  frequent  contraction  or  beat  of  the 
auricle,  (2)  the  tonus  oscillations.  The  tonus 
oscillations  include  from  twenty  to  forty  beats. 
In  the  tortoise  auricle,  the  beats  usually  become 
less  extensive  during  the  rise  of  tonus. 

The  Influence  of  "Load"  on  Ventricular  Contrac- 
tion.—  Record  the  contractions  of  the  frog's 
ventricle.  Increase  the  intraventricular  pressure 
(i.  e.  the  load  against  which  the  ventricular  muscle 
contracts)   by  clamping  the  aorta?  with  forceps 


266  THE    CIKCULATION    OF   THE   BLOOD 

the  blades  of  which  are  covered  with  rubber 
tubing. 

The  force  of  the  individual  contractions 
will  be  increased  but  their  frequency  will  be 
diminished 

The  Influence  of  Temperature  on  Frequency  of 
Contraction.  —  Let  the  drum  move  at  such  a 
speed  that  the  individual  heart-beats  in  the 
curve  shall  be  close  together,  but  yet  separate 
and  distinct.  By  means  of  a  pipette  replace 
the  normal  saline  solution  in  the  spoon  of 
the  heart-holder  with  normal  saline  solution  at 
25°  C. 

The  frequency  of  contraction  will  be  increased. 

Eeplace  the  warm  solution  with  normal  saline 
solution  at  5     C. 

The  frequency  of  contraction  will  be  diminished. 

The  Action  of  Inorganic  Salts  on  Heart  Muscle.  — 
Sever  the  apical  two-thirds  of  the  ventricle  of  the 
tortoise  heart  from  the  remainder  of  the  ventricle 
by  a  cut  parallel  with  the  auriculo-ventricular 
furrow.  With  a  second  parallel  cut  remove 
from  the  severed  portion  a  ring  two  or  three 
millimetres  wide.  Divide  the  ring  to  form  a 
strip.  Fasten  one  end  of  the  strip  to  the  short 
limb  of  a  glass  rod  bent  at  a  right  angle.  By 
means  of  a  silk  thread  connect  the  other  end  of 
the   strip  to  an  inverted   counterpoised    muscle 


nil,    MECHANICS   OF  THE   CIRCULATION      2G7 

lever  arranged  to  record  tin*  contractions  of  the 
strip  on  a  very  slowly  moving  drum. 

Sodium.  —  Immerse  the  strip  of  ventricular 
muscle  in  a  beaker  containing  0.7  per  cent  solu- 
t  inn  of  sodium  chloride. 

After  a  latent  period,  which  may  be  protracted, 
hut  usually  is  brief,  a  series  of  rhythmic  con- 
tractions will  be  observed.  The  contractions 
soon  reach  a  maximum  and  then  gradually  die 
away.  Sodium,  although  an  important  stimulus 
to  contraction,  cannot  maintain  the  ventricle  in 
continued  activity. 

The  tonus  of  the  heart  muscle  is  diminished 
by  sodium  chloride. 

Calcium.  —  Surround  a  strip  of  contracting 
ventricular  muscle  with  a  solution  of  calcium 
chloride  isotonic  with  0.7  per  cent  sodium  chlo- 
ride solution  (approximately  1.0  per  cent). 

Contractions  will  cease.  Calcium  added  to 
solutions  of  sodium  chloride,  however,  will 
lengthen  the  period  during  which  the  heart 
muscle  contracts  and  will  increase  the  strength 
of  the  individual  contractions.  Strong  solutions 
of  calcium  chloride  greatly  increase  the  tonus. 

Potassium.  —  Surround  a  non-beating  strip  of 
ventricular  muscle  with  a  solution  of  potassium 
chloride  isotonic  with  0.7  per  cent  sodium 
chloride   solution  (approximately  0.9   per  cent). 


268  THE   CIRCULATION   OF   THE   BLOOD 

Contractions  will  not  be  produced.  If  potas- 
sium be  applied  to  a  contracting  strip,  the  con- 
tractions will  cease. 

Combined  Action  of  Sodium,  Calcium,  and 
Potassium.  —  Surround  the  ventricular  muscle 
with  a  solution  containing  sodium  chloride  (0.7 
per  cent),  calcium  chloride  (0.0026  per  cent), 
and  potassium  chloride  (0.035  per  cent).  This 
is  a  modified  "  Ringer  "  solution. 

Long-continued,  rhythmic  contractions  will  be 
secured. 

Observers  are  not  entirely  agreed  as  to  the 
action  of  potassium  and  calcium  on  heart  muscle. 
The  matter  is  of  importance  because  there  is 
much  probability  that  the  rhythmic  contractions 
of  the  heart  are  the  result  of  the  constant  chemi- 
cal stimulus  of  inorganic  salts  present  in  the 
blood.  Most  observers  are  agreed  that  the  inter- 
action of  salts  of  sodium,  calcium,  and  potassium 
is  essential. 

The  fact  that  the  contraction  of  the  heart 
begins  normally  in  the  sinus  may  be  due  to  a 
greater  sensitiveness  of  that  part  to  chemical 
stimulation. 


THE  MECHANICS   OF   THE   CIRCULATION      269 


The  Heart  Sounds 

With  a  binaural  stethoscope  auscultate  the 
chest  over  its  entire  extent  during  normal  respi- 
ration and  while  the  subject  holds  his  breath. 

1.  Note  that  two  sounds  are  heard  in  the 
heart  region. 

2.  Determine  at  what  point  each  of  the  sounds 
is  most  distinct. 

It  will  be  found  that  one,  termed  the  "  first 
sound,"  will  be  most  distinct  where  the  ventricle 
comes  nearest  the  surface,  near  the  apex  of  the 
heart,  in  the  space  between  the  fifth  and  sixth 
ribs,  about  2.5  cm.  below  and  2.5  cm.  within  the 
left  nipple.  Close  inspection  of  this  region  in 
persons  not  too  fat  will  show  that  the  chest  wall 
is  raised  at  each  contraction  of  the  heart.  The 
cardiac  impulse,  as  it  is  called,  may  be  felt  dis- 
tinctly by  one  or  two  fingers  laid  in  the  fifth 
intercostal  space.  It  is  caused  by  the  rapid 
increase  in  the  tension  of  the  ventricle. 

The  "  second  sound  "  will  be  heard  most  dis- 
tinctly immediately  over  the  aortic  arch,  near  the 
junction  of  the  second  right  costal  cartilage  with 
the  sternum. 

3.  Observe  the  two  sounds  with  relation  to 
their  duration,  pitch,  intensity,  and  quality. 


270  THE    CIRCULATION    OF   THE    BLOOD 

The  first  sound  in  comparison  with  the  second 
is  of  longer  duration,  lower  pitch,  and  greater 
intensity.  The  quality  of  the  first  sound  is  dull, 
booming  ;  that  of  the  second  is  sharp,  valvular. 

4.  With  one  finger  feeling  the  cardiac  impulse 
observe  the  sounds  with  reference  to  systole  and 
diastole. 

The  first  sound  will  be  found  to  be  systolic, 
i.  e.  it  occurs  with  the  contraction  of  the  ventricle, 
while  the  second  sound  is  diastolic,  being  heard 
at  the  beginning  of  ventricular  relaxation.  The 
interval  between  the  first  and  second  sounds  is 
therefore  very  brief.  The  pause  after  the  second 
sound  before  the  first  is  heard  again,  is  consider- 
ably longer. 

The  first  sound  can  be  heard  in  the  extirpated, 
bloodless  heart  (dog).  The  contraction  of  the 
ventricular  muscle  is  therefore  alone  sufficient 
for  its  production.  But  the  sound  is  modified  or 
replaced  by  a  murmur  when  the  auriculo-ven- 
tricular  valves  are  sufficiently  injured.  It  is 
probable,  therefore,  that  the  sudden  increase  in 
the  tension  of  the  auriculo- ventricular  valves  con- 
tributes to  its  production.  The  second  sound 
obviously  is  due  to  the  sudden  increase  in  the 
tension  of  the  semilunar  valves.  It  is  replaced 
by  a  murmur  when  these  valves  are  rendered 
incompetent. 


THE   MECHANICS   OF   THE  CIRCULATION      271 

Ordinarily  the  ratio  between  the  bl l-pressure 

in  the  pulmonary  artery  and  right  ventricle  bo 
nearly  equals  the  ratio  between  the  blood 
pressure  in  the  aorta  and  left  ventricle  that  the 
semilunar  valves  in  the  pulmonary  artery  and 
aorta  close  together,  or  nearly  together,  and  their 
respective  sounds  are  heard  as  one.  Pathologic- 
ally, for  example  in  distention  of  the  right  heart 
from  prolonged  violent  exercise,  these  relations 
may  be  so  altered  as  to  produce  between  the  two 
sounds  an  interval  perceptible  to  the  ear.  The 
sound  is  then  said  to  be  reduplicated. 

The  Pressure-Pulse 

Frequency.  —  Palpate  the  radial  pulse  by 
laying  on  the  artery  at  the  wrist  the  ball  (not 
the  tip)  of  the  first,  second,  and  third  fingers  of 
the  right  hand.  The  forearm  of  both  subject 
and  observer  should  be  supported  in  a  comfort- 
able position.  Count  the  pulse  in  four  successive 
periods  of  fifteen  seconds.  The  counting  of  the 
observer's  instead  of  the  subject's  pulse  may  be 
avoided  by  noting  whether  the  subject's  supposed 
pulse  is  synchronous  with  the  observer's  heart- 
beat. 

Note  the  frequency  per  minute  when  the  sub- 
ject is  standing,  sitting,  lying,  swallowing,  hold- 
ing  the  breath;    and  before  and  after  exercise: 


272  THE   CIECULATION   OF  THE   BLOOD 

for  example,  before  and  after  lifting  the  weight 
of  the  body  ten  times  by  rising  on  the  toes. 

Sex,  eating,  the  time  of  day,  the  temperature, 
and  many  other  factors  also  influence  the  fre- 
quency of  the  pulse. 

Hardness.  —  When  pressure  is  made  upon  an 
artery  in  any  part  of  its  course,  the  pressure  is 
transmitted  in  all  directions  through  the  liquid 
contained  in  the  peri-arterial  tissues,  and  the 
artery  becomes  smaller.  Part  of  the  pressure  is 
used  upon  the  peri-arterial  tissues  themselves. 
"When  the  remaining  pressure  equals  the  maxi- 
mum blood-pressure  in  the  artery  at  the  point  of 
compression,  the  blood-pressure  on  the  distal 
side  of  this  point  will  sink  to  the  level  of  the 
blood-pressure  in  the  nearest  anastomosis.  If 
the  anastomosis  is  of  capillary  size,  the  pulse  will 
disappear.  A  pulse  which  is  obliterated  by  slight 
pressure  is  termed  "  soft ; "  if  the  pressure  re- 
quired is  relatively  considerable,  the  pulse  is 
termed  "  hard."  The  hardness  of  the  pulse  is 
therefore  a  measure  of  the  maximum  blood- 
pressure  at  the  point  of  compression,  less  the 
variable  and  unknown  quantity  required  for  the 
compression  of  the  elastic  tissues. 

Form.  — ■  1.  The  vibrations  which  follow  the 
primary  pulse  wave  cannot  ordinarily  be  recog- 
nized by  the  palpating  finger.     When,  however, 


THE   MECHANICS   OF   THE   CIRCULATION      273 

the  usual  amplitude  of  the  principal  secondary 
vibration  is  much  increased  and  the  interval  be- 
tween the  primary  and  this  secondary  vibration 
is  not  too  brief,  the  pulse  may  be  felt  to  be 
double,  or  "  dicrotic."  For  example,  dicrotism 
can  be  felt  in  some  cases  of  continued  fever. 

2.  A  pulse  which  is  felt  to  reach  its  maximum 
slowly  is  called  a  "slow  pulse"  (pulsus  tardus). 
One  which  reaches  its  maximum  rapidly,  giving 
the  palpating  finger  the  sensation  of  a  quick 
push,  is  said  to  be  a  "  quick  pulse  "  (pulsus  celer). 
Quick  and  slow  pulses  should  be  carefully  dis- 
tinguished from  frequent  and  infrequent  pulses. 

Volume.  —  The  extent  to  which  the  arterial 
wall  is  driven  from  its  position  of  equilibrium 
(volume  or  size  of  pulse)  is  a  function  of  the 
output  of  the  ventricle,  the  outflow  period, 
the  peripheral  resistance,  and  the  elasticity  of 
the  arteries.  It  is  measured  very  inexactly  by 
the  palpating  finger  and  the  sphygmograph,  accu- 
rately by  the  plethysmograph  (page  280). 

The  Pressure-Pulse  in  the  Artificial  Scheme. — 
Compress  the  pump  of  the  artificial  scheme  until 
the  arterial  pressure  is  maintained  at  50  mm. 
Hg.  Close  the  tube  leading  to  the  arterial 
manometer,  so  that  the  oscillations  of  the 
mercury  may  not  influence  the  curves  to  be 
taken.     Attach  the  small  thistle-tube   (without 

18 


274  THE    CIRCULATION    OF   THE    BLOOD 

rubber  membrane)  to  the  sphygmograph  (Fig. 
54)  and  adjust  the  tube  upon  the  aorta.  Close 
the  side  branch  of  the  sphygmograph  tube.  Bring 
the  writing  point  of  the  sphygmograph  lever 
against  a  slow-moving,  lightly-smoked  drum. 
Eecord  a  series  of  pulse  curves. 

Note  the  quick  upstroke,  corresponding  to  the 
quick  distention  of  the  artery  by  the  emptying 
of  the  ventricle,  and  the  gradual  downstroke, 
corresponding  to  the  gradual  emptying  of  the 
artery  through  the  resistance  during  the  diastole 
or  interval  between  two  beats.  Near  the  apex 
of  the  more  delicately  written  curves  may  be 
seen  a  slight  depression,  the  dicrotic  notch. 

It  is  obvious  that  the  changes  observed  in  the 
size  of  the  artery  are  the  expression  of  changes 
in  the  blood-pressure.  The  pulse  is  a  function 
of  the  blood-pressure  at  the  point  observed. 
Hence  the  term  pressure-pulse. 

The  Human  Pressure-Pulse  Curve.  —  1.  Adjust 
the  lever  of  the  recording  tambour  so  that  it  shall 
write  with  the  least  friction  possible  on  a  thinly 
smoked  drum.  Let  the  drum  revolve  slowly 
(two  revolutions  a  minute).  Be  sure  that  the 
side  branch  is  open.  Place  the  larger  thistle- 
tube,  which  serves  as  a  "receiving  tambour," 
over  the  carotid  artery,  anterior  to.  the  sterno- 
cleidomastoideus  muscle,  about  the  level  of  the 


THE    MECHANICS    OF    THE    CIB01   I. A  I  I"N       275 

thyroid  cartilage.  When  the  tambour  (Without 
rubber  membrane)  is  pressed  well  down  over  the 
artery,  let  an  assistant  close  the  side  branch.  If 
the  receiving  tambour  lias  been  properly  pliiei-d, 
the  recording  tambour  will  write  a  sharply 
marked  pulse  curve.  If  none  such  appears,  open 
the  side  branch  and  move  the  receiving  tambour 
into  a  better  position. 

Indicate  the  primary  wave,  the  predicrotic 
elevation,  and  the  dicrotic  notch. 

2.  Cover  the  thistle-tube  with  a  rubber  mem- 
brane. Cement  in  the  centre  of  the  membrane  a 
bone  collar-button.  Place  the  button  upon  the 
radial  artery  at  the  wrist  and  record  the  radial 
pulse. 

It  will  be  found  that  the  degree  of  pressure 
must  be  carefully  regulated  in  order  to  secure  a 
satisfactory  curve.  The  blood-pressure  in  the 
artery  normally  is  held  in  equilibrium  by  the 
elastic  tension  of  the  wall  of  the  artery  and  the 
surrounding  tissues.  The  pressure  of  the  sphyg- 
mograph  increases  the  tension  of  the  peri-arterial 
tissues  and  thus  assists  in  holding  the  blood- 
pressure  in  equilibrium.  The  greater  the  pres- 
sure of  the  sphygmograph,  the  larger  the  part  of 
the  blood-pressure  borne  by  it  and  the  more  ci  >m- 
pletely  will  variations  in  the  blood-press u re  be 
made   visible   in   the  pulse  curve.     The  record, 


276  THE    CIKCULATION   OF   THE    BLOOD 

however,  is  not  a  measure  of  the  absolute  blood- 
pressure,  because  it  is  not  possible  to  estimate 
accurately  how  much  of  the  blood-pressure  is 
still  held  in  equilibrium  by  the  elastic  tension 
of  the  arterial  wall  and  the  surrounding  tissues. 
The  pulse  curve  does  give  with  approximate 
correctness  the  variations  in  the  blood-pressure. 
The  correctness  would  be  complete  were  it  not 
that  the  part  of  the  blood-pressure  held  in 
equilibrium  by  the  elastic  tension  of  the  arterial 
wall  varies  with  the  size  of  the  vessel,  and  the 
size  of  the  vessel  increases  as  the  blood-pressure 
increases.  Thus  the  portion  of  the  blood-pres- 
sure which  fails  of  record  constantly  varies. 
The  error  thus  introduced  is  not  important. 
The  sphygmograph,  therefore,  gives  a  practically 
true  record  of  the  form  of  the  pulse,  i.e.  the 
time-relations  of  the  changes  in  blood-pressure. 
This  knowledge  cannot  possibly  be  secured  by 
the  palpation  of  the  pulse.  The  sphygmograph, 
it  may  be  repeated,  does  not  give  a  true  record 
of  the  absolute  blood-pressure  (hardness)  or  of 
the  amplitude  (size)  of  the  pulse.  Both  hardness 
and  amplitude  are  better  measured  by  the  pal- 
pating finger. 

In  many  sphygmographs,  for  example,  Marey's 
and  Dudgeon's,  the  pressure  on  the  artery  is 
made  by  a  metal  spring,  the  movements  of  which 


THE    MECHANICS   OF   THE   CIRCULATION'       277 

are  recorded  by  a  lever.  In  the  record  just  taken 
from  the  radial  artery,  the  pressure  was  made  by 
the  elastic  tension  of  the  rubber  membrane  clos- 
ing the  thistle-tube.  In  the  case  of  the  carotid 
artery,  this  membrane  is  replaced  by  the  skin  of 
the  neck. 

In  every  instance,  the  sphygmograph  records 
the  changes  of  blood-pressure  in  a  section  of  the 
artery  so  short  in  comparison  with  the  length  of 
the  whole  arterial  tree  as  to  be  practically  a 
cross-section. 

Low  Tension  Pressure-Pulse.  —  1.  In  the  arti- 
ficial scheme  open  slightly  the  side-branch  that 
permits  the  liquid  in  the  arterial  tubes  to  flow 
out  without  passing  through  the  resistance.  The 
arterial  pressure  will  fall  in  consequence  of  the 
diminished  peripheral  resistance.  Normally  this 
effect  is  produced  by  a  dilatation  of  the  smaller 
arteries.  Let  the  arterial  pressure  fall  to  about 
20  mm.  Hg.     Eecord  a  series  of  pulse  curves. 

Note  that  the  oscillations  of  the  mercury 
column  with  each  ventricular  beat  are  much 
higher  than  with  normal  pressure  (120-150  mm.). 
Feel  the  pulse  with  the  finger.  With  each  beat 
the  artery  quickly  expands  and  as  quickly  re- 
laxes.    The  artery  is  "softer"  than  usual. 

2.  Feel  the  normal  pulse  in  the  radial  artery. 
Note   the  normal "  hardness."     Let  the   subject 


278  THE    CIRCULATION   OP   THE   BLOOD 

inhale  two  drops  (on  no  account  more  than  two) 
of  the  nitrite  of  amyl  (to  be  dropped  on  a  hand- 
kerchief by  one  of  the  instructors).  This  power- 
ful drug  causes  dilatation  of  the  blood  vessels, 
particularly  the  smaller  arteries. 

Observe  that  as  the  face  flushes,  indicating  the 
vascular  dilatation,  the  pulse  will  be  softer. 

Do  not  repeat  the  experiment. 

Pressure-Pulse  in  Aortic  Regurgitation.  —  Empty 
the  principal  tubes  of  the  artificial  scheme.  Re- 
move the  rubber  from  about  the  aortic  valve. 
Replace  the  valve  tube.  Fill  the  apparatus  with 
water.  Compress  the  bulb  at  the  rate  and  with 
the  force  employed  to  imitate  the  normal  circula- 
tion (page  273). 

Feel  the  pulse  with  the  finger. 

After  each  systole  the  liquid  streams  back 
through  the  incompetent  valve.  The  ventricle 
is  thus  fuller  than  normal  at  the  beginning  of 
the  stroke,  while  the  arteries  are  less  than 
normally  full.  Consequently  more  than  the 
usual  quantity  is  discharged  by  the  ventricle 
into  relatively  undistended  arteries.  The  rela- 
tively lax  artery  is  thereby  quickly  and  largely 
expanded,  as  indicated  by  the  quick  thrust  given 
the  palpating  finger  and  by  the  large  excursion 
of  the  mercury  in  the  arterial  manometer. 

Record  pulse  curves. 


THE   MECHANICS   OF   Till-:   CIRCULATION      279 

The  upstroke  is  unusually  high  and  quick.  It 
is  at  once  followed  by  a  great  and  sudden  fall. 
Obviously  a  relatively  empty  artery  has  been 
suddenly  filled  by  an  unusually  large  inflow  and 
has  been  suddenly  emptied  again  through  the 
broken  valve  and  the  capillaries.  The  pulse* 
curve  shows  low  arterial  tension,  but  is  of  greater 
amplitude  than  the  pulse  in  which  low  tension 
results  from  lowering  the  peripheral  resistance. 
In  the  body,  the  amplitude  of  the  pulse  in  aortic 
regurgitation  is  increased  by  the  greater  force 
with  which  the  ventricle  contracts,  as  well  as  by 
the  larger  quantity  discharged  at  each  beat,  for 
the  back-flow  from  the  aorta  dilates  the  ventricle 
and  usually  causes  the  walls  of  the  ventricle  to 
increase  in  thickness  (dilatation  with  hypertrophy 
of  the  ventricle). 

Stenosis  of  the  Aortic  Valve.  —  Replace  the  rub- 
ber flap  upon  the  aortic  valve-tube,  and  tie  a 
string  around  the  flap  and  tube  just  over  the 
opening  in  the  glass.  Stenosis,  i.  c.  narrowing,  of 
the  opening  will  thus  be  secured.  Put  the  valve- 
tube  in  place,  and  compress  the  bulb  at  the  usual 
rate.     Eecord  pulse  curves. 

The  slow  difficult  emptying  of  the  ventricle 
will  be  evident  in  the  curve  and  to  the  hand. 
The  movements  of  the  arterial  manometer  are 
sluggish    and    of    diminished    amplitude.      The 


280  THE    CIRCULATION   OF   THE   BLOOD 

pulse  wave  is  small  and  the  upstroke  slow, 
corresponding  to  the  small  slow  inflow  through 
the  stenosed  valve. 

Eestore  the  valve  to  its  normal  state. 

Incompetence  of  the  Mitral  Valve.  —  Remove 
the  rubber  flap  from  the  mitral  valve.  Eecord 
pulse  curves  as  before. 

The  pulse  will  be  small,  because  the  pressure 
in  the  auricle  (in  this  case  the  reservoir  of  water) 
is  always  low,  while  the  pressure  in  the  arteries 
is  always  high.  Hence  the  ventricle  will  partly 
empty  itself  through  the  incompetent  mitral 
valve,  in  the  direction  of  low  resistance,  before 
the  pressure  in  the  ventricle  rises  high  enough  to 
open  the  aortic  valve  against  the  high  aortic 
pressure.  The  quantity  remaining  in  the  ventri- 
cle when  the  intraventricular  pressure  rises  high 
enough  to  open  the  aortic  valve  is  not  sufficient 
to  distend  the  arteries  to  the  normal  decree. 

In  mitral  stenosis  the  pulse  is  also  small 
because  the  narrowing  of  the  mitral  orifice  per- 
mits less  than  the  usual  quantity  of  liquid  to 
enter  the  ventricle. 

The  Volume  Pulse 

Remove  the  receiving  tambour  of  the  sphygmo- 
graph  from  its  tube,  and  insert  the  pie  thy  sino- 
graph  cylinder   (this  is  the  tube  used   in   the 


Till'.    MECHANICS   OF   THE   CIRCULA.TIOM      281 

experiment  on  the  volume  of  contracting  muscle, 

Fig.  47).  Place  the  middle  linger  in  the  cylinder, 
making  sure  that  the  rubber  collar  fits  around 
the  finger  tightly,  hut  without  impeding  the 
venous  circulation.     (Jh»se  the  side  branch. 

Periodical  alterations  in  the  volume  of  the 
finger  will  be  recorded  ;  they  have  the  rhythm  of 
the  heart-beat.  (The  friction  of  the  writing-lever 
must  be  very  slight  to  insure  success,  and  the 
curve  at  best  will  be  small.) 

Determine  the  effect  of  straining  and  forced 
respiration  upon  the  curve. 

Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Artificial 
scheme.  Microscope.  Mesentery  board.  Mercury  man- 
ometer. Aortic  cannula  <  hie  per  cent  solution  of  sodic 
carbonate.  Ligature.  Glass  rod  one  inch  long.  Frog- 
board.  Wooden  stand.  Kymograph.  Inductorium.  Dry 
cell.  Electrodes.  Key.  Electromagnetic  signal.  Sphyg- 
mograph  with  large  arm  small  thistle-tubes.  Rubber 
membrane.  Bone  collar-button.  Heart-holder.  Screw- 
clamp.  Muscle  lever  with  scale-pan  and  weights.  Stand. 
Fine  copper  wire.  Tortoise  with  heart  exposed.  Ice. 
Solution  of  sodium  chloride,  0.7  per  cent.  Solutions  of 
calcium  chloride,  and  potassium  chloride,  each  isotonic 
•with  0.7  per  cent  solution  of  sodium  chloride.  A  solu- 
tion containing  sodium  chloride,  0.7  per  cent ;  calcium 
chloride,  0.026  per  cent;  and  potassium  chloride,  0.035 
per  cent.  Binaural  stethoscope.  Nitrite  of  amyl.  Ple- 
thysmograph. 


282  THE    CIRCULATION    OF   THE   BLOOD 


X 

THE   INNERVATION  OF  THE   HEART  AND 
BLOOD-VESSELS 

The  quantity  of  blood  required  by  the  tissues 
varies  from  time  to  time.  For  example,  the 
digestive  organs  require  more  blood  when  food 
is  taken  than  at  other  times.  Variations  in  the 
blood  supply  of  the  individual  organs  are  accom- 
plished chiefly  by  varying  the  size  of  their  blood 
vessels.  To  this  end  the  blood  vessels  are  pro- 
vided with  muscular  coats  which  are  made  to 
contract  or  relax,  and  thus  to  constrict  or  dilate 
the  vessels.  The  impulse  to  contraction  or  relax- 
ation is  given  by  the  vasomotor  nerves.  It  is 
necessary,  too,  that  the  force  and  frequency  of 
ventricular  contraction  should  vary  with  the 
resistance  to  be  overcome,  the  need  for  more 
rapid  oxygenation  of  the  blood,  etc.,  and  special 
nerves  are  provided  for  this  purpose  also.  The 
control  or  innervation  of  the  heart  and  blood 
vessels  will  now  be  considered. 

The  heart  is  provided  with  nerves  that  aug- 
ment and  nerves  that  inhibit  its  action. 


INNERVATION    OF    IIKAKT   AND    ULm«U>-VI-:ssKI,S      283 

The  A.UGMENTOB  Nerves  oe  the  Eeart 

In  the  frog  both  the  augmentor  and  the  inhibi- 
tory nerves  reach  the  heart  through  the  splanch- 
nic branch  of  the  vagus.  The  augmentor  fibres 
leave  the  spinal  cord  in  the  third  spinal  nerve,  and 
pass  through  the  ramus  communicans  of  this 
nerve  into  the  third  sympathetic  ganglion,  where 
they  probably  end  in  contact  with  the  body  or 
processes  of  sympathetic  cells.  The  axis-cylin- 
ders of  these  sympathetic  cells  pass  up  the  cer- 
vical sympathetic  chain  to  the  ganglion  of  the 
vagus  (Fig.  55),  and  thence  down  the  vagus  trunk 
to  the  heart.  Thus  in  the  greater  part  of  its 
course  the  vagus  cannot  be  stimulated  without 
exciting  both  the  augmentor  and  the  inhibitory 
cardiac  fibres.  To  excite  either  alone  it  is  neces- 
sary to  stimulate  the  respective  nerves  above 
their  junction. 

Preparation  of  the  Sympathetic.  —  Cut  away  the 
lower  jaw  of  a  large  frog,  the  brain  of  which  has 
been  destroyed  by  pithing,  and  continue  the  slit 
from  the  angle  of  the  mouth  downwards  for  a 
short  distance.  Avoid  cutting  the  vagus  nerve 
(Fig.  56).  Turn  the  parts  well  aside,  and  expose 
the  vertebral  column  where  it  joins  the  skull. 
Remove  the  mucous  membrane  covering  the 
roof  of  the  mouth.     The  sympathetic  is  situated 


284 


THE    CIKCULATION   OF   THE    BLOOD 


immediately  under  the  levator  anguli  scapulae 
muscle,  which  must  be  carefully  removed.  The 
nerve  will  then  be  visible.  It  is  commonly  pig- 
mented and  usually  lies  under  an  artery.  Care- 
fully isolate  the  nerve.     Put  a  ligature  around  it 


LAS 


Fig.  55.  Scheme  of  the  sympathetic  nerve  in  the  frog.  OC.  Occiput. 
LAS.  Levator  anguli  scapulae.  Sym.  Sympathetic.  GP.  Glosso-pharyn- 
geus.  V-S.  Vago-sympathetic.  G.  Ganglion  of  the  vagus.  Ao.  Aorta. 
SA.  Subclavian  artery.  (After  Stirling's  reproduction  of  Gaskell  and 
Gadovv's  plate.) 


as  far  away  from  the  skull  as  practicable,  and 
cut  the  nerve  caudal  to  the  ligature. 

Action    of    the    Sympathetic   on    the    Heart.  — 

Arrange  the  inductorium  for  weak  tetanizing  cur- 
rents.    In  the  primary  circuit  place  the  electro- 


INNERVATION  OF  HEART  AND  BLOOD-VKSSKLS      285 

magnetic   signal.     Prepare    the    sympathetic   as 

directed  above.  Expose  the  heart  (page  75). 
Place  it  in  the  heart-holder.  Should  the  heart 
beat  rapidly,  slow  it  with  ice.  Let  the  writing 
point  record  above  the  point  of  the  electromag- 
netic signal  on  a  drum  revolving  so  slowly  that 
the  individual  beats  shall  appeal  in  the  curve 
very  close  together,  yet  far  enough  apart  to  be 
readily  counted.  Divide  the  observation  into 
nine  periods  of  twenty  seconds  each.  Place  the 
electrodes  beneath  the  sympathetic,  with  the 
short-circuiting  key  closed.  Adjust  the  heart 
lever  to  write  its  curve.  Let  the  assistant  call 
the  beginning  of  each  period  as  he  marks  it  on 
the  drum.  At  the  beginning  of  the  second  pe- 
riod, open  the  short-circuiting  key ;  at  the  begin- 
ning of  the  third  period,  close  the  short-circuiting 
key.  Lower  the  drum  when  one  circuit  is 
completed. 

Count  the  number  of  beats  in  each  period.  The 
frecmency  will  be  increased.  The  force  of  con- 
traction will  also  be  increased.1  The  latent  period 
of  excitation  is  long  and  there  is  a  prolonged 
after-effect.  The  former  frequency  is  regained 
more  rapidly  after  short  than  after  long  stimula- 
tions.    The  speed  of  the  cardiac  excitation  wave 

1  The  stimulation  of  the  augmentor  fibres  is  difficult  and 
often  fails  in  winter  frogs. 


286 


THE    CIRCULATION    OF   THE    BLOOD 


(compare  page  199)  is  increased  and  the  time  of 
its  passage  across  the  auriculo-ventricular  groove 
is  shortened,  though  this  cannot  be  observed  by 
the  method  used  in  the  present  experiment. 

The  Inhibitory  Nerves  of  the  Heart 

The   Preparation   of  the  Vagus  Nerve.  —  Fasten 
a  large  frog  on  the  board,  back  down.     Pass  the 


Fig.  56.  Scheme  of  the  cervical  nerves  in  the  frog  (after  Schenck). 
G.  P.  Glosso-pharyngeus.  Hg.  Hypoglossus.  V.  Vagus.  L.  Laryngeus. 
K.  Posterior  end  of  lower  jaw.  The  glosso-pharyngeus  has  been  drawn 
to  one  side  of  the  hypoglossus  for  the  sake  of  clearness. 

glass  tube  through  the  oesophagus  into  the 
stomach.  Eemove  the  muscles  lying  over  the 
petrohyoid  muscle,  which  passes  from  the  base  of 
the  skull  to  the  horn  of  the  hyoid  bone.     Lying 


INNERVATION  OK  HEART  AND   BLOOD-VESSELS      287 

near  the  line  between  the  angle  of  the  jaw  and 

the  auricle  are  four  nerves  (Fig.  56):  (1)  The 
hypoglossus.  This  nerve  is  superficial.  Near 
their  emergence  from  the  skull  it  is  the  lowest 
of  the  nerves,  but  later,  the  uppermost.  It  crosses 
the  remaining  nerves  and  the  blood-vessels,  and 
passes  forwards  and  inwards  towards  the  tongue. 
(2)  The  glosso-pharyngeus,  which  soon  turns  for- 
wards beneath  the  hypoglossus  parallel  to  the 
ramus  of  the  jaw.  (3)  The  vagus,  and  (4)  the 
laryngeus,  the  two  lying  almost  parallel  in  the  line 
between  the  angle  of  the  jaw  and  the  auricle. 
The  laryngeus  rests  on  the  petrohyoid  muscle,  and 
passes  upwards  and  inwards  beneath  the  arteries 
towards  the  larynx.  The  vagus  runs  at  first 
along  the  superior  vena  cava  to  the  auricle ;  a 
branch  is  given  off  to  the  lungs.  Clear  the  vagus, 
and  tie  a  silk  thread  around  the  nerve  on  the 
central  (cranial)  side  of  the  ligature,  so  that  the 
peripheral  stump  can  be  placed  on  the  electrodes 
for  stimulation.  Divide  the  laryngeal  branch. 
Keep  the  preparation  moist  with  normal  saline 
solution. 

Stimulation  of  Cardiac  Inhibitory  Fibres  in 
Vagus  Trunk.  - —  Arrange  the  inductorium  for 
weak  tetanizing  currents.  In  the  primary  circuit 
place  the  electromagnetic  signal.  Expose  the 
heart.     Place    it    in    the    heart-holder.     Let  the 


288  THE    CIRCULATION    OF    THE    BLOOD 

writing  point  record  exactly  above  the  point  of 
the  electromagnetic  signal  on  a  drum  revolving  so 
slowly  that  the  individual  heats  shall  appear  in 
the  curve  very  close  together  and  yet  far  enough 
apart  to  be  readily  counted. 

Lay  the  vagus  nerve  on  the  electrodes.  Start 
the  drum.  As  soon  as  good  curves  are  writing, 
start  the  inductorium,  and  open  the  short-circuit- 
ing key  for  about  twenty  seconds.  The  heart  will 
be  inhibited.  Xote  that  the  arrested  heart  is  al- 
ways relaxed,  i.  e.  in  diastole.  The  latent  period 
is  short  (one  or  two  heart-beats).  A  brief  after- 
effect is  present.  If  the  stimulus  is  continued, 
the  heart  will  begin  to  beat  even  during  the 
stimulation,  showing  that  the  inhibitory  mechan- 
ism can  be  exhausted.  The  heart  beats  more 
rapidly,  and  usually  more  strongly,  immediately 
after  inhibition  than  before ;  this  probably  is  due 
to  the  after-effect  of  the  stimulation  of  augmentor 
fibres  in  the  vagus  trunk,  as  explained  below. 

Repeat  the  stimulation,  but  weaken  the  stimu- 
lating current  by  moving  the  secondary  farther 
from  the  primary  coil. 

With  a  suitable  strength  of  current,  the  heart 
will  be  slowed  but  not  arrested.  The  duration 
of  diastole  will  be  markedly  less,  while  the  dura- 
tion of  systole  will  be  changed  but  little  if  at 
all.     A  stronger  excitation  would  lengthen  both 


INNERVATION  OF  HEART    \NI'   BLl 

.   The  dimiilutioD  in  i 
appears  before  the  diminutioo  in  frequency. 

Effect  of  Vagus  Stimulation  on  the  Auriculo-Ven- 
tricular  Contraction   Interval.  —  Counterpoise  two 

inverted  mna  I  Place  their  writing  points 

the  writing  point  of  th< 
magnetic   signal     Pass   fine   bent  pins  tin 

inricle  and  ventricle,  respectively,  and  con- 

a  by  silk  threads  with  the  mue 
spension  method").     Let  the  drum  revolve 
at  its  fast  1.     When  good  auricular  and 

ventricular  contractions  are  obtained,  stimulate  the 

-  trunk  with  a  current  not  <j[uite  sufficient  to 

•  arrest 
Note  that  the  inhibition  affects  both  the  auricle 
and  the  ventricle.    Weak  stimuli  affect  primarily 
the    auricles.     The   auriculo-veutricular  contrac- 
tion interval  is  lengthened. 

Irritability  of  the  Inhibited    Heart.  —  Arrest  the 

heart  by  stimulating  the  vagus  trunk.  When 
complete  inhibition  is  secured,  touch  the  ventricle 
smartly  with  the  point  of  the  seeker. 

The  ventricle  will  respond  by  a  single  contrac- 
tion. 

When  the  inhibition  is  profound,  the  irritabil- 
itv  may  be  so  far  reduced  that  the  heart  will  not 
contract  on  direct  stimulation. 

In  addition  to  bl  ly  enumerated, 

19 


290  THE    CIKCULATION    OF   THE   BLOOD 

appropriate  methods  of  observation  would  show 
that  vagus  excitation  increases  the  intraventricu- 
lar pressure  during  diastole,  lessens  the  intake 
and  the  output  of  the  ventricle,  and  diminishes 
the  tonus  of  the  heart  muscle.  The  action  of  the 
vagus  is  accompanied  by  a  positive  electrical 
variation.  The  action  on  the  sinus  and  on  the 
bulbus  does  not  differ  essentially  from  that  upon 
the  ventricle. 

It  has  already  been  pointed  out  that  the  vagus 
of  the  frog  contains  both  inhibitory  and  augment- 
ing fibres.  The  stimulation  of  the  mixed  nerve 
usually  causes  inhibition,  as  described  above,  but 
sometimes  augmentation.  The  augmentation  ob- 
served after  cessation  of  the  inhibitory  effect  is 
probably  explained  by  the  longer  after-effect  of 
the  augmentor  excitation. 

Intracardiac  Inhibitory  Mechanism.  —  Arrange 
an  inductorium  for  tetanizing  currents.  Close 
the  short-circuiting  key.  Expose  a  frog's  heart. 
Eaise  the  heart  with  a  glass  rod.  Note  the  white 
"  crescent "  between  the  sinus  venosus  and  the 
right  auricle.  Set  the  inductorium  in  action. 
Put  the  points  of  the  electrodes  on  the  crescent, 
and  open  the  short-circuiting  key  for  a  moment. 
After  one  or  two  beats  the  heart  will  stop. 

Inhibition  by  Stannius  Ligature.  —  Turn  up  the 
heart  to  expose  its  posterior  surface,  and  note  the 


INNERVATION   OF  HEABT  A.ND   BLOOD-VESSELS      291 

line  of  junction  of  the  sinus  venosus  and  righl 
auricle.  Tie  a  Ligature  around  the  heart  exactly 
at  this  line,  passing  the  thread  beneath  the  aortas, 
so  that  they  shall  aot  be  included  in  the  ligature. 

The  auricles  and  ventricle  cease  to  beat,  for  a 
time  at  least,  while  the  sinus  venosus  continues 
with  unaltered  rhythm.  (The  result  is  usually 
ascribed  to  inhibition,  from  the  mechanical  stim- 
ulation of  the  intracardiac  inhibitory  mechanism, 
[f  the  ventricle  begins  spontaneously  to  beat,  as 
may  happen  if  the  ligature  is  not  accurately 
placed,  tie  a  second  ligature  around  the  junction 
of  sinus  and  auricle.) 

Action  of  Nicotine. — Apply  nicotine  solution 
(0.2  per  cent)  to  the  ventricle.  After  a  few 
minutes,  stimulate  the  trunk  of  the  vagus  nerve. 
No  curve  need  be  written. 

The  heart  is  not  inhibited. 

Now  lift  the  heart  with  a  glass  rod,  and  stimu- 
late the  intracardiac  inhibitory  nerves. 

The  heart  is  inhibited.  Nicotine  paralyzes 
some  inhibitory  mechanism  between  the  vagus 
and  the  intracardiac  inhibitory  nerves.  But  it  is 
known  that  nicotine  does  not  paralyze  nerve 
trunks.  Hence  it  is  probable  that  the  cardiac 
inhibitory  fibres  do  not  pass  to  the  cardiac  muscle 
directly,  but  end  in  contact  with  nerve  cells, 
which     take    up     the    impulse    and    transmit    it 


292  THE    CIRCULATION   OF   THE    BLOOD 

through  their  processes  to  the  muscular  fibres  of 
the  heart. 

Atropine.  —  With  a  clean  pipette  apply  a  few 
drops  of  a  solution  of  atropine  (0.5  per  cent)  to 
the  heart.  After  a  few  moments  lift  the  ventri- 
cle and  stimulate  the  crescent. 

The  heart  is  not  inhibited.  Atropine  paralyzes 
the  intracardiac  inhibitory  nerves. 

Muscarine.  —  With  a  fine  pipette  put  upon  the 
ventricle  a  few  drops  of  normal  salt  solution  con- 
taining a  trace  of  muscarine  (a  poisonous  alkaloid 
extracted  from  certain  mushrooms). 

The  ventricle  will  gradually  be  arrested  in 
diastole,  much  distended  with  blood. 

Antagonistic  Action  of  Muscarine  and  Atropine. 
—  With  a  fresh  pipette  apply  a  little  normal  salt 
solution  of  atropine  (0.5  per  cent). 

The  heart  will  commence  to  beat  again. 

The  Centres  of  the  Heart  Nerves 

It  has  been  shown  that  the  heart  receives  in- 
hibitory and  augmenting  nerve  fibres.  The  sit- 
uation of  the  inhibitory  and  augmenting  "  centres," 
i.  e.,  the  nerve  cells  from  which  the  inhibitory 
and  augmenting  fibres  spring,  should  now  be 
considered. 

Inhibitory  Centre.  —  Place  a  frog  and  a  small 
sponge  wet  with  ether  under  a  glass  jar.    Be  very 


INNERVATION  OF  HEART  A.ND  BLOOD-VESSELS      293 


careful  aot  to  kill  the  frog  i,v  an  overdose  of 
ether.  When  insensibility  is  complete,  place  the 
animal,  back  uppermost,  on 
a  frog-board.  Cut  through 
the  skin  in  the  median  line 
from  the  nose  about  half 
way  to  the  urostyle.  I  lare- 
fully  uncover  the  roof  of  the 
skull.  Remove  the  longitu- 
dinal muscles  on  either  side 
of  the  1st,  2d,  and  3d  verte- 
bras. Strip  off  the  parietal 
bones  with  forceps,  begin- 
ning at  the  anterior  end, 
opposite  the  anterior  margin 
of  the  orbit.  Clear  away 
the  occipital  bones.  Saw 
through  the  laminae  of  the 
first  three  vertebras,  and  re- 
move the  lamime  to  expose 
the  spinal  cord.  Expose  the 
heart  by  cutting  away  tin- 
chest  wall  over  the  pericar- 
dium. Hold  the  frog  in  such 
a  way  that  the  heart  can  1"' 
observed  while  the  brain  and 
cord  are  stimulated.  "With 
needle  electrodes,  the  points  of  which  should  be 


Fig.  57.  Viewofthe  brain 
of  a  frog  from  above,  en- 
larged. L.ol.  Olfartory  liibi.-s. 
H.c.  Cerebral  hemispheres. 
G.p.  Pineal  body.  Th.o. 
Optic  thalami.  L.op.  Optic 
lobes.  C.  Cerebellum.  M.o. 
Medulla  oblongata.  s.rh. 
sinus  rhomboidalis.  (After 
Foster's  plate  in  Burdon* 
Sanderson's  Handbook.) 


294  THE    CIKCULATION   OF    THE   BLOOD 

one  millimetre  apart,  stimulate  the  spinal  cord 
with  a  tetanizing  current  of  a  strength  easily 
borne  on  the  tongue. 

Stimulation  of  the  spinal  cord  will  not  inhibit 
the  heart.  Stimulation  of  the  cerebral  hemi- 
spheres will  be  also  ineffectual.  Now  stimulate 
the  medulla  oblongata.     (Fig.  57.) 

The  heart  will  be  inhibited. 

This  method  of  locating  the  cardio -inhibitory 
centre  is  unsatisfactory,  because  the  inhibition 
produced  may  possibly  be  the  result  of  the  stimu- 
lation of  nerve  paths  to  or  from  the  centre.  Its 
results  can  be  controlled  by  the  method  of  suc- 
cessive sections,  to  be  explained  in  connection 
with  the  vasomotor  centre,  page  293. 

The  cardio-inhibitory  centre  is  always  in  ac- 
tion, for  section  of  the  vagi  causes  the  heart  to 
beat  more  frequently. 

Augmentor  Centre.  —  It  is  probable  that  this 
centre,  like  the  inhibitory  centre,  is  situated  in 
the  bulb,  but  the  location  is  not  definitely  known. 
The  constant  activity  of  the  augmentor  centre  is 
shown  by  the  fall  in  frequency  of  beat  after  sec- 
tion of  the  vagi  followed  by  bilateral  extirpation 
of  the  inferior  cervical  and  first  thoracic  ganglia 
in  mammals. 

The  neuraxons,  or  axis-cylinder  processes,  of 
the  augmentor  cells  lying  in  the  central  nervous 


INNKKVATIOX  OF  HEABT  A.ND  BLOOD-VESSELS      295 

system  pass  oul  of  the  spinal  cord  id  the  white 
rami  and  terminate  in  the  sympathetic  ganglia 
(for  example,  the  inferior  cervical  and  stellate 
ganglia  of  the  dog)  in  contact  with  sympathetic 
cells,  the  neuraxons  of  which  convey  the  impulse 
to  th«'  heart. 

The  cardiac  centres  are  readily  affected  by 
afferent  impulses  from  many  sources. 

Reflex  Inhibition  of  the  Heart;  Goltz  s  Experi- 
ment.—  Iii  a  very  lightly  etherized  frog,  expose 
the  pericardium  by  cutting  away  the  chest  wall 
over  the  heart.  Count  the  number  of  beats  in 
periods  of  twenty  seconds.  Continue  the  count 
while  an  assistant  strikes  gentle  blows  with  the 
handle  of  a  scalpel  upon  the  abdomen  at  the  rate 
of  about  140  per  minute. 

The  frequency  will  usually  diminish  and,  in  fa- 
vorable cases,  the  heart  will  at  length  he  arrested. 

Cut  both  vagus  nerves  and  repeat  the  experi- 
ment. 

The  reflex  inhibition  of  the  heart  cannot  be 
obtained  after  section  of  the  vagi. 

It  has  been  shown  by  Bernstein  that  the  affer- 
ent nerves  in  this  experiment  are  abdominal 
branches  of  the  sympathetic  nerve.  The  stim- 
ulation of  the  central  end  of  the  abdominal 
sympathetic  in  the  rabbit  also  produces  reflex 
inhibition  of  the  heart. 


296  THE    CIRCULATION    OF   THE    BLOOD 

Reflex  Augmentation.  —  Count  the  human  radi- 
al pulse  during  four  consecutive  periods  of  fifteen 
seconds.  Let  the  subject  sip  cold  water  slowly. 
Eepeat  the  count  while  the  subject  swallows. 

The  frequency  will  be  increased. 

Variations  in  the  force  and  frequency  of  the 
heart-beat  follow  the  stimulation  of  most  afferent 
nerves,  for  example  the  central  end  of  the  divided 
vagus,  the  sciatic,  and  other  mixed  nerves,  the 
nerves  of  special  sense,  and  the  afferent  nerves 
which  arise  in  the  heart  and  pass  to  the  bulb. 

The  most  conspicuous  of  the  nerves  which  bear 
impulses  from  the  heart  to  the  central  nervous 
system  in  mammals  is  the  depressor.  This  nerve 
occurs  as  an  isolated  trunk  in  the  rabbit,  and  is 
found  mixed  with  other  fibres,  for  example  in  the 
vagus,  in  many  other  animals.  The  stimulation 
of  the  end  of  the  severed  depressor  nerve  in  con- 
nection with  the  heart  is  without  effect.  The 
stimulation  of  the  end  in  connection  with  the 
bulb  slows  the  heart  and  dilates  the  blood-vessels, 
thus  causing  a  great  fall  in  the  blood-pressure. 

Thf  Innervation  of  the   Blood-Vessels 

The  Bulbar  Centre.  —  1.  Lightly  etherize  a  large 
frog.  Expose  and  cut  both  vagus'  nerves  (in 
order  to  exclude  inhibition  of  the  heart).  It  is 
of  the  first  importance  to  avoid  excessive  hemor- 


INNERVATION   OF   HEART  ANI>  BLOOD-VESSELS      297 

rhage.  Expose  the  brain  and  the  anterior  half  of 
the  spinal  cord  <  page  293  ).  Place  the  frog  on  the 
web-board.  Note  carefully  the  speed  with  which 
the  corpuscles  pass  through  the  smaller  vessels 
of  tlic  web.  The  rate  of  flow  in  the  capillaries  is 
the  best  practical  index  of  the  diameter  of  the 
small  arteries.  When  the  arteries  constrict,  the 
flow  iii  the  capillaries  will  be  less  rapid.  Remove 
the  cerebral  hemispheres  and  the  optic  lobes. 
Aiter  five  minutes  or  more  (to  allow  the  frog  to 
recover  from  the  shock  of  the  operation ),  note  the 
condition  of  the  web  vessels. 

There  will  be  no  significant  change. 

The  removal  of  the  brain  anterior  to  the  bulb 
has  not  destroyed  the  tonus  of  the  blood-vessels. 

Note  the  slow  rhythmic  changes  in  the  diam- 
eter of  the  vessels.  The  changes  are  not  uniform 
throughout  the  length  of  the  blood-vessel. 

2.  Curarize  the  frog  sufficiently  to  paralyze 
the  motor  nerves.  Stimulate  the  bulb  with  very 
weak  tetanizing  currents. 

The  How  in  the  capillaries  will  be  less  rapid. 
Obviously  the  bulb  contains  nerve  cells,  the  ex- 
citation of  which  causes  the  narrowing  of  the 
blood-vessels.  These  cells  are  termed  the  bulbar 
vasoconstrictor  centre.  Bepeated  sections  show 
that  the  vasoconstrictor  cells  are  placed  (in  the 
rabbit)  on  both  sides  of  the  median   line  from 


298  THE   CIRCULATION   OF   THE   BLOOD 

about  one  millimetre  posterior  to  the  corpora 
qnadrigemina  to  a  point  about  four  millimetres 
posterior  to  those  bodies. 

The  Vasomotor  Functions  of  the  Spinal  Cord.  — 
1.  Divide  the  cord  just  posterior  to  the  bulb. 
(A  fresh  frog  may  be  required.  In  that  case, 
remember  to  curarize.) 

The  division  of  the  fibres  connecting  the  vaso- 
constrictor centre  with  the  cord  will  be  followed 
by  the  dilatation  of  the  vessels  in  the  web  (i  e. 
the  flow  will  be  more  rapid). 

2.  Stimulate  the  peripheral  segment  of  the 
divided  cord. 

The  blood-vessels  will  constrict. 

Thus  the  neuraxons  (axis-cylinder  processes) 
of  the  bulbar  vasomotor  cells  pass  through  the 
spinal  cord  on  the  way  to  their  respective  blood- 
vessels. 

It  should  now  be  determined  whether  these 
fibres  pass  to  the  blood-vessels  without  interrup- 
tion, or  whether  they  end  in  contact  with  spinal 
vasomotor  cells  through  which  the  connection 
with  the  blood-vessels  is  made. 

3.  Wait  five  minutes  and  then  note  the  flow 
through  the  capillaries. 

The  dilatation  observed  immediately  after  the 
separation  of  the  cord  from  the  medulla  has  given 
place  to  moderate  constriction.     The  tonus  of  the 


INNERVATION   OF   HEART  AND    BLOOD-VESSELS      299 

blood-vessels  has  returned.  The  spinal  cord  has 
taken  up  the  vasomotor  function  of  the  bulb. 
Evidently   the   spinal   cord   contains    vasomotor 

cells,  which  ordinarily  arc  subsidiary  to  those  of 
the  bulh,  but  which,  when  separated  from  their 
master  cells,  acquire  the  power  of  independent 
action. 

Effect  of  Destruction  of  the  Spinal  Cord  on  t;he 
Distribution  of  the  Blood.  —  Further  evidence  of 
the  vasomotor  function  of  the  spinal  cord  is 
afforded  by  the  following  experiment. 

Expose  the  heart,  avoiding  unnecessary  loss  of 
blood.  Lay  bare  the  upper  part  of  the  intestine 
by  an  incision  on  the  left  side  of  the  umbilical 
vein,  which  lies  in  the  median  line.  Suspend  the 
frog  vertically.  Note  that  the  heart  and  the  great 
vessels  are  filled  with  blood.  Note  also  the  size 
and  number  of  the  vessels  in  the  walls  of  the 
stomach  and  intestines. 

Bend  the  frog's  head.  Put  the  seeker  into  the 
vertebral  canal  and  pass  it  gently  downwards  to 
destroy  the  spinal  cord.  The  seeker  will  move 
easily,  if  really  in  the  canal.  Look  at  the  heart 
and  great  arteries. 

The  heart  will  soon  be  bloodless,  though  beating 
regularly.  Examine  the  vessels  of  the  stomach 
and  intestine.  They  are  distended.  Evidently, 
the  contents  of  the  heart  and  the  great  arteries 


300  THE   CIRCULATION   OF  THE   BLOOD 

have  passed  into  dilated  smaller  arteries  and 
veins.  It  would  be  found,  on  waiting,  that  this 
effect  is  not  a  passing  consequence  of  inhibition. 
The  destruction  of  the  spinal  cord  has  changed 
the  distribution  of  the  blood. 

The  Vasomotor  Fibres  leave  the  Cord  in  the 
Anterior  Roots  of  Spinal  Nerves.  —  1.  Remove 
the  arches  of  the  5th,  6th,  7th,  8th,  and  9th  ver- 
tebras and  lay  bare  the  cord  in  a  large  frog  in 
which  the  motor  nerves  have  been  paralyzed  with 
curare.  Note  the  capillary  flow  in  the  web.  On 
the  side  on  which  the  web-vessels  are  examined, 
tie  a  silk  thread  around  each  of  the  anterior  roots 
near  their  origin  from  the  cord,  and  sever  the  roots 
between  the  ligature  and  the  cord. 

The  vessels  will  dilate. 

2.  Stimulate  the  peripheral  ends  of  several  of 
the  divided  roots. 

Constriction  will  follow. 

The  vascular  dilatation  which  follows  the  de- 
struction of  the  spinal  cord  is  not  permanent. 
After  a  time  the  vessels  regain  their  tonus.  It  is 
probable,  therefore,  that  vasomotor  nerve  cells 
exist  outside  the  spinal  cord,  and  this  conclusion 
is  confirmed  by  the  results  gained  on  warm-blooded 
animals  with  the  nicotine  method.  Langley  has 
found  that  the  injection  of  about  ten  milligrams 
of  nicotine  into  a  vein  of  a  cat  will  prevent,  for  a 


INNERVATION  OF  HEART   AND   [ILOOIi-VESSELS      301 

time,  the  passage  of  nerve  impulses  through  sym 
pathetic  cells.    Painting  the  ganglia  with  nicotine 
has  the  same  effect.     In  animals  the  sympathetic 

cells  of  which  have  thus  been  paralyzed,  the  stim- 
ulation of  the  lumbar  nerves  in  the  spinal  canal 
produces  no  change  in  the  vessels  of  the  genera- 
tive organs,  though  in  animals  not  poisoned  with 
nicotine  this  stimulation  causes  marked  constric- 
tion. The  lumbar  vasomotor  fibres  must  there- 
fore end  in  connection  with  sympathetic  nerve 
cells  which  transmit  the  constrictor  impulse  to 
the  blood-vessel.  Similar  observations  in  other 
regions  warrant  the  belief  that  all  the  vasomotor 
fibres  emerging  from  the  spinal  cord  end  in  like 
manner. 

Thus  the  vasoconstrictor  system  probably  con- 
sists of  three  neurons.  The  first  is  a  sympa- 
thetic cell,  lying  apart  from  the  central  nervous 
system.  Its  neuraxon  (axis-cylinder  process) 
passes  directly  to  the  blood-vessel.  The  second 
is  a  spinal  cell,  the  neuraxon  of  which  leaves  the 
cord  and  terminates  in  contact  with  the  sympa- 
thetic cell  or  its  branches.  The  third  has  its 
cell  body  in  the  bulb  and  its  neuraxon  termi- 
nates in  contact  with  the  second   neuron. 

Commonly,  as  for  example  in  the  nerves  of  the 
extremities,  the  sympathetic  neuraxon  passes 
from  the  ganglion  along  the  gray  ramus  into  the 


302  THE    CIRCULATION    OF   THE   BLOOD 

corresponding  spinal  nerve,  in  which  it  continues 
to  its  distribution. 

Vasoconstrictor  Fibres  in  the  Sciatic  Nerve.  — 
Curarize  a  frog  sufficiently  to  paralyze  the  volun- 
tary muscles  (any  excess  of  curare  will  paralyze 
the  vasomotor  fibres  also).  Carefully  destroy  the 
brain  with  the  seeker,  avoiding  loss  of  blood. 
Expose  the  right  sciatic  nerve  for  a  short  distance 
on  one  side,  using  the  greatest  care  not  to  injure 
the  blood-vessels.  Tie  a  thread  tightly  around 
the  nerve  near  the  upper  end  of  the  exposed  por- 
tion. Lay  the  frog,  back  upward,  on  the  web-board, 
placing  the  web  of  the  right  foot  over  the  notch, 
and  securing  it  with  fine  pins.  Examine  the  web 
under  a  low  power,  to  make  sure  that  the  circu- 
lation has  not  been  interrupted  by  stretching  the 
web.  Place  the  secondary  at  such  a  distance 
from  the  primary  coil  that  the  induced  current 
shall  be  barely  perceptible  to  the  tongue.  Set 
the  hammer  vibrating,  and  close  the  short-circuit- 
ing key.  Put  the  electrodes  under  the  sciatic 
nerve  on  the  peripheral  side  of  the  ligature.  Let 
a  second  observer  watch  a  small  vessel  of  the  web 
through  the  microscope.  Open  the  short-circuit- 
ing key  for  a  moment  only. 

The  blood-stream  slows  from  constriction  of 
the  supplying  vessels,  the  contraction  increasing 
during  a  few  seconds  and  then  subsiding. 


INNERVATION  OF   HEABT  AND  BLOOD-VESSEL8      303 

This  experiment  requires  much  care  and  i 

observation.  The  curare  effect  must  be  very 
slight;  a  small  quantity  of  the  drug  should  be 
given  an  hour  before  the  observation  is  made. 
Great  pains  must  be  taken  to  use  feeble  currents 
and  not  to  prolong  the  excitation,  for  the  vaso- 
motor nerves  are  rapidly  exhausted.  The  nar- 
rowing of  the  arteries  of  the  web  is  usually 
evident  only  in  the  slowing  of  the  blood-stream 
during  excitation. 

Vasodilator  Nerves.  —  1.  Repeat  the  preceding 
experiment  in  a  frog  in  which  the  sciatic  nerve  has 
been  four  days  severed  (without  injury  to  the  fem- 
oral vessels).  On  stimulation  of  the  peripheral 
segment  of  the  divided  sciatic  nerve,  the  vessels 
of  the  web  will  dilate  instead  of  constricting. 

Evidently  the  sciatic  nerve  contains  vasodilator 
as  well  as  vasoconstrictor  fibres.  When  the 
sciatic  fibres  are  separated  from  their  cells  of 
origin  by  the  section  of  the  nerve,  the  fibres  distal 
to  the  section  degenerate.  But  the  degeneration 
does  not  proceed  at  the  same  rate  in  all  the  fibres. 
The  vasoconstrictors  die  before  the  vasodilators. 
In  ordinary  stimulation  of  the  normal  nerve  the 
action  of  the  constrictors  overpowers  that  of  the 
dilators.  In  the  partially  degenerated  nerve, 
the  same  stimulation  causes  dilatation  because 
the  constrictor  fibres  are  dead  or  dying. 


304  THE    CIRCULATION    OF   THE    BLOOD 

2.  Note  the  rate  of  flow  in  the  web-vessels  in 
the  uninjured  limb.  Stimulate  the  sciatic  nerve 
with  the  single  induction  current  repeated  at 
intervals  of  five  seconds. 

The  vessels  of  the  web  will  dilate. 

The  vasoconstrictor  and  vasodilator  fibres  also 
react  differently  to  cold.  If  the  hind  limb  (cat) 
be  cooled,  the  stimulation  that  normally  causes 
vasoconstriction  will  cause  vasodilatation. 

Vasoconstrictor  and  vasodilator  fibres  are  not 
always  found  in  the  same  nerve-trunks;  in  the 
chorda  tympani  nerve,  for  example,  there  are  only 
dilator  fibres. 

The  central  relations  of  the  dilator  nerves  have 
not  been  sufficiently  studied  to  warrant  their 
discussion  here. 

Reflex  Vasomotor  Actions.  —  1.  Note  the  rate 
of  flow  in  the  vessels  of  the  web  in  a  lightly 
curarized  frog.  Stimulate  the  skin  (not  too  near 
the  bulb  or  cord)  with  tetanizing  currents.  The 
stimulus  must  not  be  repeated  often,  or  fatigue 
will  obscure  the  result. 

Keflex  constriction  of  the  vessels  will  take  place. 
The  sensory  impulse  is  carried  by  afferent  fibres 
to  the  vasomotor  centres. 

Eepeat  the  experiment,  using  in  place  of  the 
electrical  a  mechanical  stimulus,  such  as  pinching 
the  skin  with  forceps. 


INNERVATION   01   BSABT  AND  BLOOD-VESSELS      305 


Apparatus 

Normal  saline.  Bowl.  Towel.  Pipette.  Glass  plate, 
luductoriura.  Key.  Wires.  Dry  cell.  Electrodes. 
Needle  electrodes.  Frog-board.  Electromagnetic  signal. 
Heart-holder.  Kymograph.  Glass  tube  for  oesophagus. 
Two  muscle  levers.  Solutions  of  nicotine  (0.2  per  cent), 
atropine  (0.5  per  cent),  muscarine  (a  trace  in  normal  salt 
solution).  Curare.  Ether.  Sponge.  Glass  jar.  Ver- 
tebral saw.  Web-board.  Fine  pins.  Microscope.  Frog, 
the  sciatic  nerve  of  which  has  been  severed  four  days. 
Millimetre  rule.     Silk  thread. 


20 


INDEX 


Absolute  force  of  muscle,  224. 

Action  current,  heart,  173,  175;  human  muscle,  172;  in  brain 

and  cord,  182;    muscle,  166;    nerve,  178;  optic  nerve,  181; 

precedes  contraction,  174;  speed  of,  177;  tetanus,  168. 
Alcohol,  action  on  nerve,  136. 
Alteration  theory,  164. 
Amalgamation,  21. 
Anode  and  cathode,  13,  71,  93. 
Aortic  regurgitation,  278. 
Aortic  valve,  stenosis  of,  279. 
Apparatus,  criticism  of,  53;   lists  of,  11,  49,  58,  122,  128,  149, 

193,  234,  281,  305. 
Artificial  scheme  of  circulation,  243. 
Atropine,  action  on  cardiac  inhibition,  292. 
Augmentor  centre,  294. 
Augmentor  nerves  of  heart,  283. 
Auriculo-veutricular  contraction  interval,  263 ;  effect  of  vagus 

stimulation,  289. 
Bernstein's  apex  experiments,  259;  rheotome,  176. 
Blood  pressure,  curve,  251  ;  peripheral  resistance,  253. 
Brain  of  frog,  dorsal  view,  293. 
Bulbar  vasomotor  centre,  296. 

Calcium,  action  on  contraction,  126;  on  heart  muscle,  267. 
Capillary  electrometer  (see  Electrometer),  14. 
Carbon  dioxide,  action  on  nerve,  134;  apparatus,  135. 
Cathode,  13. 


308  INDEX 

Cell,  electrical,  21,  24,  27. 

Cells,  in  series,  94. 

Centres  of  heart  nerves,  292. 

Cervical  nerves  in  frog,  286. 

Circulation,  artificial  scheme  of,  243 ;  capillary,  297 ;  in  frog's 
mesentery,  248;  mechanics  of,  239;  rate  of  flow,  248. 

Compensation  method  of  measuring  electromotive  force,  158. 

Compensatory  pause,  261. 

Conductivity,  129  ;  changed  by  galvanic  current,  82. 

Contraction,  affected  by  direction  of  current,  118  ;  idiomuscular, 
127  ;  isometric,  219  ;  law  of,  75,  95  ;  of  human  muscle,  twitch, 
220;  opening  and  closing,  61  ;  tonic,  70,  102. 

Contraction  time  of  clear  and  turbid  fibres,  198. 

Contraction  wave,  201  ;  form  influenced  by  strength  of  stimu- 
lus, 203. 

Contracture,  203. 

Cork  clamp,  65. 

Curare,  poisons  motor  end-plates,  132. 

Daniell  cell,  24. 

Degeneration,  reaction  of,  97. 

Demarcation  current,  150,  159,  161;  as  stimulus,  153;  causa- 
tion, 161  ;  electromotive  force  of,  157  ;  interference  with  stim- 
ulating current,  155;  muscle,  150;  negative  variation,  178; 
nerve,  159;  positive  variation,  179. 

Depressor  nerve,  296. 

Dicrotic  notch,  273. 

Differential  rheotome,  176. 

Distilled  water,  as  stimulus,  124. 

Dry  cell,  27. 

Drying,  as  a  stimulus,  110,  125. 

Du  Bois-Reymond,  molecular  hypothesis,  162. 

Duchenne's  points,  89. 

Elasticity  and  extensibility  of  a  metal  spring,  229 ;  of  a  rubber 
band,  230  ;  of  skeletal  muscle,  230. 

Electrical  stimulation,  12. 

Electrical  units,  14. 

Electric  fish,  192. 


INDEX  309 

Electrodes,  for  human  nerves,  91  ;  indifferent,  74;  DOB-polar- 
i/.able,  59,  60;  platinum,  31. 

Electrolyte,  20. 

Electrolysis,  27. 

Electromagnetic  induction,  83. 

Electromagnetic  Bignal,  68. 

Electrometer,  14,  17,  21,  28,  2'.»,  .10. 

Electrotonic  current,  I86j  as  stimulus,  191  ;  negative  ami  pos- 
itive variation,  188;  polarization  increment,  188. 

Electrotonns,  81. 

Engelmann's  incisions,  262. 

Ergograph,  220. 

Excitation  wave,  199;  remains  in  original  fibre,  143. 

Exclusion  of  make  or  break  curreut,  43. 

Extensibility,  229,  281. 

Extra  contraction  of  heart,  261. 

Extra  currents  in  imluctorium,  41. 

Fatigue,  human  skeletal  muscle,  233 ;  polar,  108 ;  skeletal 
muscle  of  frog,  232. 

Flexors  and  extensors,  relative  excitability,  139. 

Frog  board,  115. 

Frog,  brain,  293  ;  muscles  of  hind  limb,  7,  62. 

Galvanic  current,  59. 

Galvani's  experiment,  12. 

Galvanotropism,  98. 

(las  chamber,  135. 

Gaskell's  block,  263  ;  clamp,  263. 

Goltz's  experiment,  295. 

Gracilis,  145. 

Graphic  method,  51. 

Heart,  action  current,  17.3,  175;  action  of  inorganic  salts  on, 
266;  action  of  sympathetic  on,  284  ;  augmentor  nerves,  283; 
anricnlo-ventricnlar  interval,  263;  change  in  form,  257; 
chemical  theory,  268;  compensatory  pause,  261;  constant 
stimulus,  261;  contraction  curve,  258;  extra  contraction, 
261;  Gaskell's  block,  263,  holder,  174:  impulse,  269;  in- 
fluence of  load,  265 ;  influence  of  temperature,  266 :  inhibi- 


310  INDEX 

Heart  —  (continued) 

tion,  253 ;  inhibition  by  Stannius  ligature,  290  ;  inhibition  by 
vagus  stimulation,  287  ;  inhibitory  nerves,  286 ;  intra-cardiac 
inhibitory  mechanism,  290 ;  irregularities  explained,  262,  264 ; 
irritability,  261 ;  irritability  during  inhibition,  289 ;  isolated 
apex,  259  ;  maximal  contractions,  258  ;  method  of  exposure, 
75;  muscle,  spontaneous  contraction,  260;  nerve  free,  131; 
outflow  period,  256;  polar  inhibition,  114;  polar  stimulation, 
73 ;  reflex  augmentation,  296  ;  reflex  inhibition,  295 ;  refrac- 
tory period,  261  ;  sounds,  269;  tonus,  265;  transmission  of 
contraction  wave,  262 ;  transmission  of  excitation,  263 ; 
valves,  241,  244,  255,  278,  279,  280;  various  effects  of  vagus 
stimulation,  290. 

Human  muscle,  artificial  tetanus,  221 ;    natural  tetanus,  221  ; 
isometric  contraction,  220. 

Human  nerves,  stimulation  of,  89. 

Idio-muscular  contraction,  127. 

Induction,  unipolar,  44.  i 

Induction  currents,  30,  40,  119 ;  in  nerves,  43. 

Inductorium,  31,  35  ;  graduation,  38,  39. 

Inhibition  by  galvanic  current,  114 ;  of  heart,  253. 

Inhibitory  centre,  292. 

Inhibitory  nerves  of  heart,  286. 

Innervation  of  blood-vessels,  296. 

Inorganic  salts,  influence  on  contraction,  266. 

Intestine,  polar  stimulation  of,  67. 

Ions,  13,  26. 

Irritability,    6,  129;    separable   from    conductivity,  134;   polar 
changes,  78. 

Isometric  method,  217. 

Isometric  spring,  graduation  of,  218. 

Key,  short-circuiting,  31 ;  simple,  31. 

Kymograph,  51. 

Latent  period  of  muscle,  197. 

Lines  of  force,  33. 

Load,  influence  on  contraction,  265 ;  on  height  of  contraction, 
204. 


INI'KX 


ill 


Magnetic  Held,  33. 

Magnetic  induction,  30. 

Make  and  break  currents,  exclusion,  48  ;  as  stimuli,  40. 

Manometer,  mercury,  252. 

Mitral  incompetence,  278,  280. 

Moist  chamber,  60. 

Molecular  hypothesis,  1G2. 
Monopolar  stimulation,  74,  93. 
Motor-points  of  forearm,  90,  91 ;  stimulation,  92. 
Muscarine,  action  on  heart,  292;  antagonistic  to  atropine,  292. 
Muscle,  action  current,   166;  damp,  9;  clear  and  turbid,  140; 
curve,  196;  curve,  for  estimating  total  work  -lone,  226;  de- 
marcation current,  150;  electromotive  phenomena,  150;  in- 
dependent irritability,  130;  influence  of  structure,  140;  lever, 
55,  60;  preparation  of  gastrocnemius,  4  ;  sound,  211. 
Muscle  warmer,  206. 
Myomeres,  Rosenthal's  scheme  of,  162. 
Negative  variation,  178;  of  secretion  current,  184. 
Nerve,  action  current,  178;  conducts  in  both  directions,  144; 
demarcation  current,  159;  electrical  resistance,  190;  electro- 
motive  phenomena,    150;    fibres,   relative   excitability,  139; 
holder,  9 ;    induction   in,  43  ;    irritability,  142 ;    polarization, 
187;  polar  stimulation,  75;  specific  irritability,  141  ;  stimu- 
lated by  own  demarcation  current,  160. 
Nerve  impulse,  11 ;  periodic  discbarge,  105  ;  speed  of,  146. 
Nerve-muscle  preparation,  4,  6,  8,  9. 
Nicotine,  action  on  cardiac  inhibition,  291. 
Nitrite  of  amyl,  277. 
Normal  saline,  126. 
Opening  and  closing  contraction,  61. 
Optic  nerve,  action  current,  181. 
Paper,  smoked,  method  of  using,  52. 
Paradoxical  contraction,  191. 
Paramecium,  galvanotropism,  98. 
Peripheral  resistance,  250. 
Pletbysmograph,  280. 
Point  of  view,  4. 


312  INDEX 

Polar  fatigue,  108. 

Polar  inhibition,  heart,  114;  veratrinized  muscle,  116. 

Polarization,  23,  25,  59  ;  current,  25,  87,  106;  increment,  188. 

Polar  refusal,  155. 

Polar  stimulation,  109, 112;  by  induced  current,  120;  of  muscle, 
65,  73 ;  of  nerve,  75,  93. 

Pole-changer,  25. 

Positive  after  current,  180. 

Positive  variation,  107,  179. 

Potassium,  influence  on  contraction,  267. 

Potassium  iodide  method  for  determining  direction  of  current, 
27,  119. 

Potential,  electrical,  13. 

Pulse,  dicrotic,  273;  form  of,  272;  frequency,  271;  hardness, 
272 ;  in  regurgitation  and  stenosis,  278,  279 ;  pressure  curve, 
274 ;  volume,  273. 

Refractory  period,  261. 

Rheocord,  20. 

Rheoscopic  frog,  166. 

Rheotachygraph,  177. 

Rhythmic  contraction,  heart,  103;  skeletal  muscle,  104,  126. 

Rhythmic  discharge  of  nerve  impulses,  105. 

Rigid  muscle  lever,  205. 

Ringer  solution,  268. 

Ritter-Rollett  phenomenon,  139. 

Ritter's  opening  tetanus,  110. 

Saline  solutions  as  stimuli,  125. 

Sartorius,  144. 

Secretion  current,  negative  variation,  183,  184. 

Self-induction,  41. 

Shortening  in  single  contraction,  and  in  tetanus,  215. 

Single  contraction,  195;  duration  of  periods,  196. 

Smooth  muscle,  simple  contraction,  222;  spontaneous  contrac- 
tions, 221  ;  tetanus,  223. 

Sodium,  influence  on  contraction,  267. 

Sphygmograph,  256. 

Spinal  cord,  destruction  changes  distribution  of  blood,  299. 


INDEX  313 

Staircase  contraction,  heart,  259. 

Stand,  9. 

Strumitis  ligature  inhibits  heart,  290. 

Stimulati effected  by  current  angle,  118;  by  form  of  muscle 

117. 

Stimulation,  chemical,  81,  no,  124;  constant,  may  cause  peri- 
odic contraction,  126;  drying,  110,  125;  electrical,  12,  59; 
human  nerves,  89  ;  mechanical,  5,  9,  \j7  ;  monopolar,  74,  93; 
motor  points,  '.'2. 

Stimuli,  6;  summation,  138. 

Stimulus,  changes  in  intensity,  62 ;  influence  of  duration,  100; 
minimal  and  maximal,  137;  threshold  value,  187. 

Strength  of  .stimulus,  related  to  form  of  contraction  wave,  203. 

Stroboscopic  method,  168. 

Superposition  in  tetanus,  210;  of  two  contractions,  209. 

Surface  tension,  15. 

Sympathetic,  action  on  heart,  284;  in  frog,  284;  preparation 
of,  283. 

Synchronous  points,  method  of  obtaining,  84. 

Temperature,  influence  on  contraction,  205,  266. 

Tetanizing  curreuts,  42. 

Tetanus,  43,  128.  168,  209;  opening  and  closing,  108. 

Time  relations  of  developing  energy,  226. 

Tonic  contraction,  70,  102. 

Touus,  265. 

Total  work  done,  224 ;  estimated  by  muscle  curve,  226. 

Tuning  fork,  55. 

Unipolar  induction,  44  ;  stimulation,  48,  183. 

Ureter,  polar  stimulation  of,  66. 

Vagus,  preparation  of,  286 ;  stimulation  inhibits  heart-beat,  287  ; 
stimulation  lengthens  auriculo-ventrieular  contraction  inter- 
val, 289. 

Vasoconstrictor  fibres  in  sciatic  nerve,  302;  system,  301. 

Vasodilator  nerves,  303. 

Vasomotor  centre  in  bulb,  296;  functions  of  cord,  298;  fibres 
in  anterior  roots  of  spinal  nerves,  300;  reflexes,  304. 

Veratrine,  influence  on  form  of  contraction,  208. 


314  INDEX 

Volume  of  contracting  muscle,  194. 

Volume  pulse,  280. 

Volume  tube,  195. 

Wallerian  degeneration,  97,  131. 

Wheel  interrupter,  167. 

Work  adder,  225. 

Work  done,  influenced  by  load,  223. 

Writing  point,  56. 


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